I have had a bump on my back for a few months that looks like a blood blister, I have popped it like a blood blister and it went but came back?

Blocked gland? A sebaceous cyst is a collection of oily fluid that occurs when an oil gland is blocked. Some folks are more prone to them than other and they often appear on the neck, shoulders, and back. Try to avoid skin products that are oily. Please see doc. IF it is a cyst, he/she can remove it. The sack must be removed otherwise it is likely to refill. Peace and good health.
Cherry angioma. See a dermatologist. Easy to cure.