peanut butter?

I had a peanut butter sandwich this morning and a glass of milk (cheesey huh?) because I was going to eat dinner at my in-laws today and didn't want to fill up. I've been having this strange pain on the left side since about a half hour after eating. Has anyone ever had anything like this happen before? I thought at first it was gas but it hasn't gone away after swallowing a beano. I know it's surely not a heart problem because if it was, it wouldn't hurt for a few seconds then disappear for an hour and come back suddenly for the same amount of time.