Hello and welcome.
There ARE medical conditions which cause sex to be painful no matter what position, no matter what is used. I would suggest a physical check up with your gyno doc to rule out any physical problems.
For the last six years of her life sex was painful for my Mom. My parents stopped having sex because of this. My dad talked to the doctor the other day to find out if her cancer could have been the cause of this. The doc said it was a distinct possibility.
My mom was a very private person so wouldn't bring this up with her doctor therefore it was never looked after. If she had brought it up when sex first became painful she might be alive today.
Yes, you need to get the psychological aspect looked after but please get the physical looked after as well. Maybe the cover on your clit is missing or doesn't quite cover the clit which would cause painful stimulation. Please, get yourself checked out. I would hate to have someone else miss a big problem because they couldn't talk to their doctor about sexual problems.
As for what's the purpose or point of sex. For me it's the added level of intimacy, the mental/emotional connection. There is absolutely no way I have an orgasm every single time I have sex, not even 1 in 10 times! There are times when I get very little out of sex at all but I do it because it's not all about me. His needs need to be met as well. If either of my boyfriends want sex & we have the time I'll oblige simply because they oblige me when I need it and they don't. I love them both & for me doing something simply because it's something they want right then and there is part of who I am. It doesn't always work this way but when we have the time and the need, why not? There are many more ways to have sex than simply insertion.
There are as many ways to do polyamory as there are people practicing it!