What is wrong with me?

Okay, I am engaged and have been deeply in love with my fiance. Sometime a couple weeks ago, I abruptly got very anxious and came down with the stomach bug. Since then, I can't shake the feeling that I'm smothered. I'm getting cold feet but I don't want to. I want to make the relationship work and I want to feel happy again. I feel better when I first wake up and throughout the day, but towards the evening I get very anxious again and sometimes I feel sick. I can't shake it. I also have anxiety about a few other things that I have dealt with recently. Is this something that will pass or could it be clinical or a chemical inbalance? Its driving me crazy...