20 Years old with ED? Not performance anxiety related...

Hey all. This is somewhat nightmarish. 

I am 20 years old, and have had been intimate with several women over the past couple of months. All has been fine until these recent 2-3 weeks. It started with my penis having less girth (usually very wide) and difficulty becoming hard at home when wanting to masturbate. 2 nights ago I realized it has become worse. My current lady was grinding against me at the house of blues, then we went upstairs to a private room, and even though we were just making out, I was curious if I could get hard, and I couldnt. She doesn't know this, since we were justing kissing. 

Even when I am able to become somewhat erect it is usually "half-mast" meaning that while my penis is usually anywhere from 7 1/2 and 8 inches, it is now a little over 6!! Also the girth has lessened significantly as well. I am deeply distressed by this, I just woke up after having nightmares about this very issue. 

Anybody who can offer some advice? My research has netted a few caused, the most probable being stress related? I don't know if I have increased stress over the past few weeks, especially since I just netted a replacement job finally @ circa 75k. I feel like my health is great, I bike 5 miles a day, drink atleast 200 fluid ounces of water, eat vegitarian, and don't smoke.

Thanks guys....