What Causes Heart Burn After Taking Mirtazapine?

Is there a problem in taking mirtazapine 15 mg and a supplement that I recently began taking for heartburn that has L-5-Hydroxyytrytophan in it (25 mg per pill)? It also has 450 mg of D-limonene and 3 mg of Melatonin per pill. I was taking 1 pill, but have take 2 the last few nights. I have been having gastro symptoms that seem to be getting worse - upset stomach for awhile and haven t been able to determine why. Thank you