Stomach Pains After Eating...

This is nothing critical but it has become rather annoying:

often after I have something to eat (even after eating very little), I find that I get stomach pains when undergoing any physical activity. This is especially true when I do something such as walking my dog. The best way I think I could describe it is having "a rock in my stomach." it's usually at a concentrated spot in the lower part of my stomach. It gets worse the longer I exert myself. It seems occur most when I do something that will shake up my stomach. I've talked to a couple of people about it and they've all said they've never had anything like this. Should I be concerned about this? Could this be an ulcer perhaps? I remember having this problem for at least a year now (maybe longer) so it's nothing that new. The pain goes away after a few minutes of rest so it really isn't more than a nuisance. I'm pretty good at ignoring pain and wouldn't have any problem doing so. However, my only worry with this is whether or not i'll be doing damage to my stomach by continuing to exert myself.

What do you think guys? Should I talk to a doctor or is this normal? I've always imagined "cramps" to be what one gets if one has diarrhea, and this is not at all like that.

Thanks for your advice!