I doubt you are alone. I have known many people that have this problem with various sports. It would be hard to narrow down to one thing to reference, but exercise and the chemicals and/or hormones associated can have a harsh effect on your body. The real benefits or exercise is in the recovery.

If you are curious, start with epinephrine and it's effect on the system. If you really just want it to stop, experiment with food and times of eating. Try cooling down the intensity. I don't know if you are new to this or how good your fitness level is, but exercise causes blood to move away from the GI tract. It could be that the blood moving back in post workout is kick starting your GI tract. You might just be sneak attacking yourself, so to speak.

But, you did ask about lactic acid. Lactic acid is normal in the body. Exercise at high intensity causes spikes in lactate levels is more an indication of the buffering system not being able to keep up. This is an indication that you are doing anaerobic work as opposed to aerobic work, which is in a zone where the buffering system is working at similar rate to lactic acid release, so there is minimal build up.

Really, you probably eat more acidic foods on a regular basis and certainly your stomach acid is more acidic than the drop in acidity in your blood stream. Your blood stream just can not get significantly lower than pH 7 without killing you. So, the buffer system is always working, even if it needs time after the fact to catch up. You might try a more alkaline diet or supplementing with bicarbonate contains substances. Realistically, you might just being doing too hard, too long or having a bad reaction to your eating plan though.

somewhere in here I just confused myself, doh. I hope you will at least find some keywords to search.