Anxiety with Relationship

I'm dealing with some anxiety and I'm not entirely certain what its source is.

I don't have a history of anxiety or depression in my life. In the past I've always handled stress very well. I'm 21, graduated from college, with a fantastic job in graphic design that I take a great deal of pride in. I consider myself pretty healthy, smart, and attractive, and recently started dating a girl who has brought nothing but good into my life. We balance each other out very well; Im somewhat pessimistic and reserved, and she's very optimistic and outgoing. We have a great mix of common interests and differences that keeps things interesting and our chemistry is awesome. I love her more than anything, and she's always been there for me.

That being said, about 4 days ago we had a small argument over creationism in schools. We have differing opinions on religion, but neither of us are firmly set in our beliefs or really know what we believe. Despite this, that argument triggered a massive bout of anxiety. For days now my stomach has been in a knot about it. When I'm not around her, the anxiety just hovers around, I dont want to eat, I dread being alone with my thoughts, I have no drive to get out and do anything (Whereas normally Im an obsessively productive person), but when I see her or think about her, the anxiety sort of spikes. There is just a twinge of anxiety and nausea whenever I think about her, or see things that make me think about her.

The thing is, while she is the trigger, she's not the problem. There are no problems in our relationship, I still want her around (Ive been in a situation where I dont love someone anymore, and theres that disconnection and wanting to be away from them) and this isn't that. Despite that she triggers the anxiety Im still strongest around her. I love her and can't imagine being without her. I can't pinpoint WHAT is actually the thought that provokes the anxiety. I don't think she's going to cheat on me, I trust her, I dont have any specific worries about us, and I want to be with her. However, its difficult to be around her when she triggers the anxiety. I have no sexual drive anymore, I can't eat, and when I do its in small, small portions with a great deal of nausea, and its impossible for me to focus on work.

I guess what I want to know is if anyone has any advice on fixing or managing this?

I had anxiety once before, last year, when I broke up with my last girlfriend, and then had second thoughts about that. I tried to patch things up with her for awhile and the whole time I was panicked about losing her for good, but this anxiety was targeted. I knew what was causing it and could ignore or focus on the problem as I needed to.

Now, I have no idea what the actual source is. Our differences in religion dont bother me, both of my past relationships were the same way and that never bothered me. We have very similar values and interests and have been incredibly happy together.

I do not know what to do, but I can't lose what I've got.

I went to a clinic today and got some anti-anxiety meds today to stop the panic/anxiety attacks until I can get this figured out.

Please help.

We have tried discussing it, but it doesn't really go anywhere as Im not really sure what to discuss. I can't figure out what is causing the anxiety, I just know I get a sick-to-my-stomach feeling of anxiety whenever I think about her, and I can't link it to anything in specific, its just THERE.

I dont really have any stress relief practices since Ive never really responded to stress in the past. Typically its just been laying out my priorities, since the only stress Ive ever responded to was work-related.