I agree with FrozenGirl - start slowly and gently, do not push yourself too hard at first and in particular be gentle with your abdominal area. And I also agree that aerobics can also be problematic - angry guts don't usually like to be jostled around, and anything high-impact can also be problematic if you have joint pains/arthritis. If you find you're able to do gentle yoga or slow, short walks, then you can gradually try to increase the intensity & length of your exercise and see how that goes. Definitely start off slowly though and listen to your body - if something hurts or feels uncomfortable, then skip that and try something else. Don't push yourself too much especially at first. Also, and I know this is a bit difficult to do, but don't compare yourself to others. What someone else is able to do exercise-wise may be totally different from what you're able to do - your health picture is unique from anyone else's, so try not to compare yourself to others (in particular, don't feel bad if you can't do something that it seems like you should be able to do, even if it's something that others can easily do). Just focus on yourself and what you can do, and don't feel bad if there's something you can't do.
(I say that last part from experience - my mother runs marathons, but due to my hip arthritis I can't even jog a half mile without a lot of pain, so running just doesn't happen for me. If I think too much about how I can't jog then I feel sad, particularly when compared to my mother's many running achievements, but I can do other things like ride my bike without pain, so I try to just focus on that instead - I can ride my bike and I enjoy it and it's fine with my hips, so I just ignore that other stuff and plan fun bike rides for myself. Focus on the positive!)