What Causes Excessive Stomach Gas Immediately After Eating?

Question: Latly; within the last month, mostly each time I eat I get gas within minutes, smells like rotten egg, worst when I eat fatty food - I have NEVER had this problem sometimes it is accompanied with lower ab pain (colic) and when I go to the bathroom I feel better, other times it is just gas.

Back ground: About 2 months ago my daughter had a fund raiser of dark chocolate covered pretzels, I probably ate 5 pretzels a day for 1 month, along with coke cola and I know this is not healthy - but it was winter

Hat happen, my stool started changing, got dark, soft, very sticky, I was leaving long streaks of stool on the toilet -

I have since stopped eating dark chocolate covered pretzels, about 1 month without eating them, and started eating better and now my stool is back to brown, still a little sticky but not like before, and I leave very small streaks

BUT I still get very bad gas when I eat almost anything
and if I eat anything fatty I go to the bathroom - not diarrea just soft.

If I eat very clean for a couple of days, yogurt (no milk or cheese) apples, bananas, rice, and very little meat the gas stops, and my stool firms up, but If I go back to eating a fatty diet the gas comes back immediately

Background: in the past I had reflux - no longer - high stress life and job - little exercise - work sitting down for long periods of time - I have a demanding job - technologist and kids so I have little time and low motivation and I am prone to anxiety and worry

I have an appointment with my doctor in 2 days - is this serious ?