We are ttc. is gas/flatulance a common predictor of ovulation or an early sign of conception?

No: Common signs are: clear crystalline stringy cervical mucous, and some women actually have a painful sensation or "mittelschmerz" when they ovulate. In general though, if you don't need to worry about it. If you are have sex just 2-3 times a week there are always sperm in your tubes. You don't need to "time" sex. That can take some of the fun out of it.