Mr bojangles is my best buddy he is my heart and my mother's I got him for my mom and he not eating as much and we are worried

He is a black male pug I believe he is about 3 years old he will skip a meal here and there and be fine but yesterday he was not feeling well I noticed a little bit on his back leg we put a little peroxide On it and I'm worried that he is not doing well today I am going to give him a bath he didn't eat breakfast yesterday so please any comments would help we love him so much we already lost a pug right before him and we can't do it again my kids love him especially when he comes over they adore him we all do please tell me what I should do any comments or questions I would appreciate it a lot