My 6 month is super gassy, always farting and burping. She wakes up crying and screaming sometimes and squirms while nursing. What could be the cause?

Change moms diet. If she is being exclusively breastfed, look at your diet. The mothers diet can cause the baby to sometimes be gassy. Avoid starches, beans and other gassy veggies. If you are supplementing with formula she may be having some intolerance to the formula. She may need to be changed to a different formula. For formula changes you should see your pediatrician or a peds GI doctor.
Normal. That is most likely normal. Have her try mylicon drops to help with the gas, but if not better, see your doctor.