Seconded almost as strongly as I possibly can, but with added caveats! I was a bean pole for my entire life, struggling to gain weight. The answer was simple: I wasn't giving my body the signal to gain muscle by lifting some HEAVY weights. I read Starting Strength and followed the program. I put on ~30lbs over 3-4 months, and got WAY strong. That's after having done crossfit for at least 5-6 years. I took my squat from 185lbs to 300lbs.

It took 2 months of rereading the squat chapter, filming myself, correcting myself, etc, before I finally got that one down. Now that I understand it, I can spot faults in others, but it took a while for it to click. Rereading the dbook helps, though a couple of Rippetoe's coaching cues set me on the wrong path. A starting strength specific coach can straighten you out in just a couple of sessions. DON'T think any other certification, personal trainer, or coach is a substitute, they are NOT.

Don't do starting strength for a year. (If it takes you that long to do the novice linear progression, you are definitely doing something wrong.) Rippetoe's advice for intermediates is pretty marginal IMO and you can't possibly stay a novice for a year doing the program.

Switch to Barbell Medicine's "the bridge" instead of resetting the weights a second time.