I don't know about the belly swelling but the thing on her incision looks like a abscess - so basically a collection of pus. Seeing this thread made me remember that Tiki actually had the same thing. It got bigger over time and I did end up taking her to the vet but what he basically did was just to pop it and put on some antibacterial cream and then told me to keep an eye on it, keep her from messing with it, and if it didn't heal I'd get a prescription for antibiotic pills. As far as I remember that was not needed.
So yeah, I don't know if you'll need to see a vet about it. It might just heal up on it's own.

When Taggart was neutered he also took a quite while to heal but I sprayed his wound with an aloe vera spray (all natural) which helps healing and also cooled down the area so he was more comfortable. Maybe you could do something like that to help with the healing?