Help: Unfamiliar Stomach Episode

Good morning

Chronic lifelong stomach pain sufferer. Most foods I would eat and immediate be in the bathroom. Was tested for Crohns, Celiac, etc through Colonoscopy. Nothing Was put on a low FODMAP diet a few years ago and it’s been a life saver. If I stay on the program I’m good. About five weeks ago I started at a new gym to lose body fat and increase muscle. So I’m still for the most part doing the FODMAP diet just in more quantities- the only change has been Casein Protein. For the last week I’ve been having this before bed . Had no issues for a week - starting Friday and the reason I’m here today was a very unfamiliar crampy stomach ache - it lasted Saturday but still somewhat dull and mild- by Saturday night I had body aches and still a stomach ache and it’s worse . I can go to the bathroom it’s normal solid stools- any opinions would be great - the unfamiliar feeling of this stomach ache , the length of it ,and the body aches are concerning me. No fever - Normally my stomach issues end quickly.
My mother says I was lactose intolerant as a kid but honestly I’ve had ice cream, etc over the last many years without issues The casein protein has me concerned cause it’s the only change . Am I just catching a bug ? Being paranoid ? Would love some thoughts

Bruce