My bf is always mad at me for lil things why?

my bf gets mad at me for little things that seem unimportant he thinks I ignore him but I don't I never would. I told him I was going to the doctors weds on friday and I needed to reduce my stress (my doctor's orders) So i never texted him today or anything like I usually do so he told me that I was ignoring him..and then he gets mad at me for using my other aim sn because he thought I told him I don't use it but I never said that I just said it wasn't working at the time but it is. Now why is he getting mad over this? Is he being controlling he gets mad like this often and he wants to have for the first time together and I'm worried to because if he gets mad like this I mean he can't be like this when we get ual, What do I do?