What should you do if you have BC-BS insurance and you're 20 and in college and it drops when you're 22 and you have an autoimmune disease and is there a way you can stay under it?

If it drops when you turn 22, having an autoimmune disease doesn't change that, but you may be eligible for COBRA or HIPAA for an extended amount of time. It may be wise to try to enroll in an employer group health plan and not have any gaps in coverage so it won't be considered a pre-existing condition.