DOES THE Depo shot cause stomach problems?

It could do anything. Even if it is not listed in the common side effects, even the drug companies don't know what their drugs do 100%. Weight gain is a common side effect for Birth Control. Anything that messes with your hormones can cause stomach problems and a number of other things. Talk it over with your Dr., and don't drink anything with phosphoric acid since Depo has been linked to some bone density problems.