You are getting stronger and a bit heavier; surely most of that weight is muscle. Some refer to this phenomenon as bulking up. You might subconsciously have a bias when you look in the mirror, as you stand a little straighter, you suck your gut in a bit, and square your shoulders. You could be fooling yourself.
Several years ago I used to weight myself at the health club where I worked. I was the heaviest I had ever been. No problem, I was the strongest I had ever been. Instead of asking if I once played basketball people would ask me if I had played football.
Shortly after that I went to work at a different health club. They had no scale, but when they did get one I was told it was five pounds off. The scale indicated 250, so I subtracted five pounds to get 245 pounds. I had gained an additional five pounds. Still no problem, I was bulking up and getting stronger.