Please help me

I'm a 26 female I'm 6 feet 2 and I weigh 423 and my lower back hurts it's fine when sitting but when I bend over or start doing stuff it bugs but tonight it really hurts is it because I'm fat ?

Yes. It probably hurts because of your weight.  But it COULD be something else,  so talking to your doctor about it,  if you haven't already,  is probably a good idea. Good luck. 

Probably. I was 335 at my highest and doing dishes at the sink caused me lots of back pain, I knew it was the weight of my abdomen. Even sleeping on my stomach caused some pain. I debated buying a stomach binder to 'hold up' the weight. That's when I realized this had got out of hand and decided on WLS. No back pain since.

Only a physician can tell you why you are suffering from back pain. Unfortunately, many doctors are quick to blame any problem on your weight, so finding a doctor who doesn't immediately dismiss your pain can be difficult to find.

Personally, back pain was the motivating factor for me to pursue WLS. I was in pain all the time. My days were filled with hunting for the next place I could sit to alleviate it. After I lost weight, the pain greatly diminished and I have days with absolutely no pain. Plus, the discomfort I feel now is manageable and not constant.

Something going on in there and the weight just irritates it more!  I would get it checked!