If it's just in the afternoon and goes back down overnight it sounds like it's mainly gas.
Have you thought about some probiotics? They might help you digest food without being so gassy.

Eating slowly, light exercise, chewing food thoroughly and avoiding gassy food (ie yeast, cabbage, beans, artificial sweeteners, carbonated drinks) can help. Try google for a proper list of foods that cause bloating.

Try drinking peppermint tea or camomile tea. You can also buy charcoal and other things to reduce gas at the chemist.