I think I can answer some of your questions, although I actually had Hodgkin's Lymphoma, not breast cancer. The effects of chemo can be slightly different depending on the type of chemo (type of poison used, b/c that's exactly what it is) and it can also be different for the same type of chemo, but each person can have a slightly different response. What I can give you are guidelines & it's likely to be true for you - just not 100% exactly the same b/c it can be different by type & by individual response.
After I would have a chemo treatment, starting a few hours afterwards, I would have increased nausea. The nausea would pretty much completely go away by the 5th day after treatment. I had chemo once every two weeks for 6 months. The nausea medications were very helpful, but I always thought that I had more nausea than most people. But, even still, it really wasn't that bad. I only threw up twice during the entire 6 months. Much more common was getting nauseous suddenly & dry heaving until the medication could take effect. This typically happened b/c I waited a little too long before taking the medication again.
As for absorption of the nausea medication - one of the pills was absorbed through the mucous membranes of my mouth, called odansetron. You place it against the inside of your cheek & it dissolves. Takes about a minute. Doesn't taste bad (not like candy, either), just not that bad. That medication, the odansetron, worked awesome. For me, I think it worked better than the other medication, prochlorazine, b/c that one was a swallowed pill. Remember, I did not have a gastric bypass, I had the duodenal switch & they really are very different in terms of medication. I have a fully functioning regular stomach that is just smaller in volume, but I still digest inside the stomach like normal. I absorb far less in the small intestine than bypassers, though. That's why I don't think the swallowed pill, prochlorazine, was as helpful to me as the odansetron. For you, you will absorb more of it than I did so long as it doesn't upset your stomach so that you throw it up. Will that happen? I don't think so, though can't be sure. I remember a couple of the oncologist doctors talking to me about it right before I started treatment & they were only familiar with banders or bypassers & they said that, in their experience & opinion, I wouldn't have any more trouble keeping it down than I would my regular vitamins.
My advice would be to definitely ask for odansetron, even if you're not prescribed it & cite your WLS as why you need it. It's much more expensive than prochlorazine. The best thing to do is to take both & then you can "flip flop" them. Each of them can only be taken every 6 - 8 hrs so if you monitor taking them on time well, you should be fine with eating something before taking your prochlorazine - or whatever oral pill to swallow they give you. I would definitely get the odansetron, though!
As for WL - it will likely continue so long as you're still in your WL window UNLESS you're also taking heavy amounts of steoroids. I was given a steoroid with each chemo dose, but only in the IV with the actual chemo, otherwise I didn't have to take it. I know other people (who didn't have WLS), but are cancer survivors who have complained about gained 10 - 30 pounds from a combination of steoroids & decreased physical activity b/c of the effects of treatment. Fatigue is a very, very real thing & affects upwards of 90% of people. Your body will be undergoing a lot of stress in the next few months & NEEDS adequate nutrition. Please, do not try to overly limit what you eat - just eat healthy & let your body get the nutrition it needs to (literally) survive & be healthy. If you're still in your WL window, you will likely continue to lose weight, but honestly, that shouldn't be your main priority right now. Surviving is.
As for exercise, I would strongly suggest to continue exercising, but you will likely find that you can't do as much - that's completely normal. There's a lot of research that suggests exercising during cancer treatment helps to control fatigue & also helps your mood.
I would also strongly suggest that you join a cancer treatment group. There are things you can discuss with them that you will find helpful b/c you don't have to worry about your family's feelings &/or the fact that others who love & support you ultimately can't exactly relate to what you're going through. I believe Gilda's Club is also in Canada. You can also try googling it with your city name or ask the cancer center social worker for support resources.
Hope this helps :) Good luck with everything & write if you need/ want, I'm always willing to help!
Lisa
HW / SW / CW / GW 299 / 287 / 159.8 / 140 Feb '09 / Mar '09 / Feb '13 /Aug '10
Appendicitis/Bowel Obstruction Surgery 8/21/10
Beat Hodgkin's Lymphoma! 7/15/2011 - 1/26/2012 

I LOVE MY DS!!!