Keep getting erections in therapy

I’m asking you guys not to make any jokes and if there’s any advice for this uncomfy situation. This is really affecting my therapy sessions and it makes me feel so sick and unclean. It keeps happening when I talk about anything traumatic. Not even sex related. I can’t do this over and over. I start talking about my trauma I feel myself getting hard and I can’t focus anymore because I’m disgusted. I stop talking and spend the rest of the session in silence and I know that’s not useful. Im not turned on. I don’t want this to happen. My therapist is a woman and I don’t want her to think I’m being inappropriate. I don’t want her to find out.