Had the same trouble. Zero padding left on my stomach, just skin. Shots were painful and nothing happened. Switched to the saddlebags where there's actual tissue - works again! Injection pain stopped too. Huge difference overall.
18 months on tirzepatide, built up to 15mg and held it for 4 months. Took a month off at 15mg and came back at 5mg. During the break I added 200 calories daily with lots of protein, kept away from processed stuff. Didn't have issues with hunger or cravings. Restarted at 5mg and felt it kick in...