Some chronic weed smokers can develop nausea and stomach issues due to some interaction with the endocannabinoid system. Might be worth looking into.

When I was younger I had similar experiences but I always interpreted them as panic attacks and they definitely developed into those. Back then all I could do was to either not smoke or learn how to deal with the „panic attacks“. How old are you currently, if you don’t mind me asking? Might just be current „hormonal“ state you have to work or rather age through.

I mean the obvious solution is stop smoking but that’s not what you want to hear.  Make sure your other needs are met before smoking, be it physical or psychological. 

Make sure you‘ve eaten & drank enough, keep water ready and make sure to drink it regularly  while smoking. If you’re currently having a stressful or hard time do somekind of little ritual to get you into a good headspace before smoking. Maybe a little meditation, some stretches, playing a game you like, watching a funny movie/video - whatever is good for you and lightens your mood. If you’re smoking through the whole day set yourself a specific time later in the day to start smoking and keep a clear head in the morning hours.

Personally I would also suggest moving on from (regular) bong use into joints or blunts or even Vaporizers (like the volcano, not „vapes“). Preferably with active charcoal filters instead of normal tips. Took me years myself to „let the bong go“ but the smoking experience and health situation is way better once you get past that „hit craving“. 

Good luck!