Can't lift my baby

Last night was rough. My 2.5 month old baby was particularly needy last night so I was up for 2.5 hours straight feeding, soothing, diaper changing, repeat. 3 poop explosions. Anyway, my back completely gave out during this chaos and I had to call my husband in to lift the baby because I am now physically unable to lift my baby. I went to the doctor today because I obviously need to be able to lift my baby. My husband is working and can't help me all the time. They said it's just a pulled muscle and should heal in a few weeks.

I'm going to have to suck it up, take some tylenol and deal with this somehow until it heals. I have no idea what I'm going to do if my back gives out again. I have a PT appointment but it is 3 weeks out. What the heck am I going to do. My baby is a hearty 16 pound chonker and I am a small woman. He's only going to get heavier and I obviously need to figure out a way to strengthen by back and core quickly, or learn how to not injure my back. I guess I'm just worrying / ranting but if anyone has some advice I would gladly take it