Is it normal to suddenly develop an intolerance to foods when you've had no issue with them before? Is it a pregnancy thing?

Twice now I've eaten onions and ended up in agonizing pain during the night, doubled over, gassy and have to bolt for the loo. Onions have never been an issue before, and I'm happy to eradicate them out of my diet, but will I be able to eat them again? We use them a lot!

Any stories for me? TIA.