Is It Safe To Take Melatonic For Anxiety Disorder?

I have an anxiety disorder in which I have had a long standing prescription for Clonezepam .5 mg max daily dose of two tabs per day. I usually take 1/4 to 1/2 of a tablet at one time, usually at night because I have trouble sleeping. Lately, I have decided to try Melatonin 1 mg instead. I had the Clonazepam the night before but not the last two nights, so I haven't taken it in two days. It worked pretty well but I noticed that I had quite a bit of mucus in the back of my throat when I awoke. Last night I noticed that I could hardly breathe through my nose as I was falling asleep. This was a bit unnerving to me and caused a bit of anxiety. I don't want to use the Clonezepam but I am afraid I might be allergic to whatever is in the Melatonin. I have many allergies including corn, gluten and dairy. I'm pretty strict about the gluten but not so with other things. Is there a form of Melatonin I can take that comes in a more pure form that I might tolerate better?