My girlfriend is having her period. What can I do?

The most stupid but sincere way is to express your feelings to your girlfriend and let her feel your intentions.

You said that you really don't know what to do except feel distressed. In fact, the answer is simple. You just need to let her know that you are distressed and care about her. You can try your best to comfort her, hug her and take care of her.

You can tell her to have a good rest, bring her things to relieve symptoms, tell her a few jokes to make her feel better, and tell her that you will come to see her often and accompany her when you have time to make her feel safe ...

If you do the above, you will be a qualified and caring boyfriend. There are any other ways you can think of to make your girlfriend happy and comfortable, you can try. I believe your girlfriend will be very moved and grateful to you after you have done these actions of caring for her, and then your relationship will get better and better.