Hi, im new to the gym and i did a bad back woerkout and it hurts for 3 weeks. what do you think happend?

Overdid it: Its normal 2 feel a little sore after 1st starting in the gym, but if u overdo it, u can get hurt. 3 weeks of back pain is 2 long and is a signal something is wrong, a strain, sprain or worse. To avoid injuring yourself further and 2 find the proper course of treatment see ur doctor, and then follow up with physical therapy or a certified trainer as medically directed to avoid further injuries.

Too hard too soon?: Did you train all-out that first time? When first starting a weight training regimen, it's important to start with very light weights and focus on the form of the movements to start conditioning the body properly. If you went too heavy, you could have strained the muscles.