I Am 48 Year Old Male. I Have Had A

I am 48 year old male. I have had a very noticed while riding long distance on my road bike my stomach is very sensitive, almost to the point of queasy and very uncomfortable. And recently, I have had diarrhea. That, however, had started soon after a cold and when I started a more strict diet for calorie restriction. Have always ate relatively healthy.
May not be related, but have in the last few years had issues of my stomach cramping pretty intensely while doing any type of core/sit up workout. Workout doesn't have to be that intense but I feel it cramp quickly. I may even have soreness that feels like I have stomach flu a few days after doing workout.
Please advise. Thank you