5 year old gets upset very easy she is very clingy and doesn't catch on as quickly as her twin could she have a learning or behavioral issue?

Possible: Tough to say, but most commonly, early behavioral issues are first diagnosed by the parents. Studies have all shown the importance of early diagnosis and intervention also. It may be simple "sibling rivalry" and a cry for attention in a 5yo, but you can not go wrong having her evaluated by a pediatric behavioral specialist to be safe. Good luck.

Talk to her teacher,: Sunday-school teacher or day-care provider to determine if the behaviors impact her learning &/or peer interactions in those settings. if you perceive a problem, there's a 90% chance you're right. Call your school district's Child Find Team for an evaluation for eligibility for Early Childhood Special Ed & seek referral to a Developmental/Behavioral Pediatrician & child psychologist