Im 29wks pregnant & have been experiencing stomache pains followed by diarrhea on daily basis, is this common? could this be due to current heatwave?

Unlikely: It's unlikely that your stomach pains and diarrhea are caused by heat wave. More likely that they are caused by a viral gastroenteritis. Pregnancy causes your immune system to be suppressed a bit, and things that you could have eaten or tolerated when not pregnant, can cause illness when you are pregnant. Make sure to drink a lot of water and stay hydrated. If continues, see your doctor.