my whole life i lived w/o knowing i had a gluten allergy. (or celiac, i dunno).

now at 30 i decided to get some bloodword done to see if i had a food intolerance, IBS or whatever causes my bloating or constipation.

can these thing just come on, all of a sudden?

Yes, celiac is often triggered by a trauma to the body - illness, stress, injury, pregnancy, etc.