Can't finish!!

My boyfriend and I have been together for almost year. The sex is amazing but there's an issue, I can't finish. I have been on an antidepressant that is known for lowering ones sex drive and making it harder to finish.  I can tell I get really close and usually he has to stop because I get so tense and shake and such. I know the issue is my medication but does anyone have any tips on how to help this?