Reta makes me tired and lost muscle. Going back on Tirz

I was on mounjaro for 2 years. Went from 225 lbs to 188-192ish and stayed in this range for about a year and maintained. Then I added Reta and within 5 weeks went from 188 to 177 yet my stomach didnt get noticeably leaner. A few friends I havent seen in a while told me I look like I lost some muscle as I had a good amount of it from 2 decades of lifting.

I didnt believe them as I look lean but I got a tape measure and low and behold my arms lost an inch in size which is alot. Also in Reta I seem to be tired throughout the day. I am thinking to get back on Tirzepatide