Solange -- I'm Under Attack ... By My Face!

Solange Knowles looked great during her wedding, but after the reception she broke out in hives ... and by process of elimination, she's either allergic to shrimp, or Jay Z.

It doesn't seem to be a case of nerves ... Beyonce's sister's face appeared smooth and radiant in the wedding photos ... but after the reception -- when she got in a car with Jigga -- all hell broke loose on her face.

According to our sources, Solange suffered some kind of food allergy, though she isn't sure what it was from. We're told the hives were gone in a matter of minutes.

Solange got hitched in New Orleans Sunday -- she married music video director Alan Ferguson.

Rough.