Track your macro nutrients for a few days and (GASP!) your calories. I felt like I have been loosing strength so I looked at a few of my usual eating days. While my fat intake was good (I didn't feel hungry) my protein was way too low for me to build/maintain muscle. I was only eating about 40 to 50g of protein. I should be eating around 80g. I also found out that I was only eating about 1200 ~ 1400 cal a day. I'm trying to up that by 500cal. I know a cal is not just a cal, I'm burning fat, but my strength is suffering for it. So yeah, track your nutrients. Make adjustments. See how it goes.
Edit: That 500 more cal is definitely going to come from meat! Mmmm meat.
Starting weight: 180lbs
Current weight 130lbs