allergy to beer?

could i be allergic to something in beer? I used to be able to drink beer, any kind and i would be fine.
But in the past 6 or 7 months i have started to get very  sick after only 2 or 3 beers, the next day i am  in and out of the bathroom every 10 to 20 min. i have extreme bowel issues and feeling like i could vomit. this last for the majority of the the day and then im fine by night. I know that a gluten allergy can make you feel like this, however i can still eat wheat and breads and other things made with wheat and i feel just fine. its only when i drink beer that i feel this way. Is there anything else in beer that i could be allergic to that would give this kind of reaction?

thanks.