Idly has urad dal/black gram in it. That along with the fermentation sometimes makes you feel bloated.
I don't think sambar will make you feel bloated, it's the idly which will make you feel bloated.
Don't drink water in between eating idlys. Also avoid eating outside idlys as they might contain soda in excess.
Next Steps
eat idly in a little less quantity. also don't drink milk or coffee before eating idly
when you feel bloated drink hot water. you can also drink jeerakarishta after breakfast and dinner everyday. that will help to improve your digestion.
Health Tips
drink hot water before going to bed and early morning. also don't eat idlys at night