Embarrassed to take shirt off???

I know this is weird, but I’ve been with my boyfriend for a little over a year now, and every time we have sex I don’t take my shirt off.

I have a couple times, but not majority and definitely not recently.

I think this has to do with a couple of reasons.

Mainly, I’m not comfortable w my body. I feel overweight, I’ve gained nearly 15 lbs and weigh in at 155 lbs.

Also, I have a birthmark on my right arm and I always wear long sleeves. I don’t think he has ever seen it but once at the beach last summer.

Thirdly, we always do the same position because he only wants to do doggy.

I know it’s odd but does anyone have any advice? I don’t even go in public w a short sleeve even if it’s 100 degrees out lol

I don’t know where to start...