Feeling insecure about my body

I recently went back to work and started new routine of going to the gym near my workplace. I noticed because I work in an educational setting, most of the people going to the gym are students. They are very young like 18 or 19 years old and have very fit and toned bodies. I just feel insecure when I see them. I try to hide my body and I feel like I’m secretly being judged. I feel fat and old. I am 31 years old.

I just don’t know what’s wrong with me. I feel like everything is a competition and I am beating up myself for it although I lost 34lbs in the last 3.5 months. I just seem to never be satisfied and there’s always someone out there who’s doing everything better. I feel like I am playing catch up here again.

I would love to get some advice on how to help myself out of this situation. I don’t want to hide at the back of the spin room anymore. How can I feel better?