My (23f) boyfriend (22m) thinks I'm making excuses at the gym

Hello, I'm on my period right now and I am not performing well at the gym today. We spent the morning preparing differently; He made shakes for us and I was cleaning the bedroom. By the time he was ready to workout, I had only eaten a rice krispy and drank hydration and caffeine water. He has mentioned previously a lot of times that I take too long to get ready for events, so I thought he would be annoyed if I needed more time to get ready and we just decided to go. We started working out together and I just wasn't pushing as much weight as he wanted me to and I needed to use the bathroom a lot because of the stomach issues I was having, but he thought I was making excuses. He also got mad when I started yawning, but I told to him that I have less energy on my period and did not eat much compared to him today. How can I explain to him properly that I just wasn't in the best condition to workout and that I'm not trying to make excuses?
Tldr: I am not as strong at the gym rn and my bf thinks I making excuses. How do I properly explain myself?


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