So do you think the vit D could be actually giving me a problem ? I thought to stop the vit D and see how I react then. I take b12 early in the morning on empty stomach and take vit D in the afternoon with food. The cramps last night were like I never had in my life, started in lower abdomen right after eating dinner, and later it was lower and upper abdomen, lasted for a few hours ( not very bad in the beginning ) then it went away, I even had a banana before going to bed. 4 years ago I started taking vit D3 5000 IU but it was giving me constipation so I stopped ( and never did try again taking it until now, that's why this time I started with 1000 IU ).