Having an orgasm!?

 So I'm 19, I recently lost my virginity, about three months ago. Anyways I love my SO, and usually when we're having sex he'll drive me to the edge where I feel like I'm going to orgasm but (I've never had one) like I feel like a lot of pressure builds up in my stomach and I feel this tingly sensation (like a very good one) but it feels like I'm going to pee if I let go. (Like I won't even need to go pee) but  It feels wonderful but I can't seem to let my self go, like I'm worried that I'm going to end peeing or something. . . Any tips on letting go? Is this actually what orgasm would be? Like it just feels so good I guess I might be over thinking everything!? Help thank you!!!