I got a seasonal allergy shot and like one min after the shot i've had some horrible middle through lower back pain. is this suppose to happen?

Unusual: It would be helpful to know more about your immunotherapy history (what is in the shot, how often do you get injections, is there a build-up phase, etc). This is an unusual symptom in isolation, but the timing in relation to the shot cannot be ignored. A virtual consult on HealthTap with an experienced Allergist is an option. Your doctor needs to know about the reaction (call today).