There is a ton of shit you can do at home to build strength. Also eating heavy protein diet. Get those calories up, way up. 4k+ a day.

The gym obviously is the best place to be. But you can start with various types of pushups, situps, leg exercises, etc at home.

Here's a crazy one. Go in your hallway, back and feet to wall, feet straight spread just an inch past shoulder length. Put your hands straight out in front of you at shoulder level, fingers straight out palms flat to ground. Don't let your hands drop below shoulder level the entire time. Lean forward just enough that your back and shoulders are not touching the wall, it's OK if your ass touches. Now squat 50 times or keep going until it hurts enough you can't anymore. Take 30-60s, repeat, 30-60s, repeat.

By the time you're done you should feel a burning sensation in your lower back, shoulder area, and legs.

I was like you once. The day I stepped in the gym I was doing push ups with my feet above my head perpendicular to the wall lifting my entire body weight.

Get creative. Lifting weights is an entire different feeling and practicing good technique. But you really can build a ton of strength at home and get your muscles used to the stress.