Lifting box and went to stand and felt my lower back pop a few times. couldn't stand up straight for awhile now it hurts to move. any suggestions?

Get checked out: This may be a simple muscle strain, a herniated disc, or something more serious. Same thing happened to me and I just rested, took Motrin, used heat for a few days and it did improve a bit. I then took a short course of oral steroids and had a therapist work on my back. The therapist basically told me i was way out of shape and helped me with exercises that really helped. You should see a doc