Headaches from Jello?

I am still on my post op clear liquids diet. My surgeon told me Sugar Free jello would be fine. But it feel like every time I eat it (Which has only been 3 times) I get a pretty decent headache. Anyone else experience this? Looking forward to full liquids tomorrow! WOOP WOOP

Could it be from the aspartame?  I know I can not have anything with that in it because I get a horrible headache from it.  

I am allergic to red dye 40, which is in lots of things including many flavors of jello. It gives me a massive migraine...

Aspartame (nutrasweet) gives me a MIGRANE headache. I cannot have it.