I have a cross bite, but treatment was purely cosmetic. Random popping/pain in jaw when laughing, eating, etc my mouth gets stuck open at times. Help?

Not cosmetic. Obviosly your problem is not just cosmetic, ie: your TMJ dysfunction. If it doesn't look right it doesn't work right, and vica versa. Please seek evaluation with a fully qualified Orthodontic Specialist, or seek examination in the Orthodontic Department of a University Dental School.
See a Dentist, TMJ. Latest research disputes the popular belief that braces can trigger TMJ disorders. If you suffer from all of these symptoms, there are chances you have TMJ problems. See your dentist for consultation and referral to OFP specialist if needed.