You know it could be a underlying gastric problem like gerd or hyperacidity. You might try using an acid blocker like Pepcid before riding. Or you could try an anti GERD (gastric reflux) like Prilosec. I have problems with both. Intervals did not bother me but hard centuries were always a problem until I started using the above. Of course, it is quite likely that you do not have a similar problem. But it only costs a few $$$ to see if the stuff helps.