Reason For Reoccurring Symptoms Of Giardia And How Can It Be Treated?

I was diagnosed with Giardia a few years back and was prescribed Nitacure (BD for 3 Days) and Nex-OZ (BD for 5 days). I took this course once but since the problem reappeared in 2-3 months, I repeated the course. I have repeated this course several times in a year for last 2-3 years. When I take the medicine, it has the effect of immediately ending stomach bloating , ending my irregular (and sometimes loose) motions, reducing my excessive sleeping (I would wake up absolutely fresh after 5 - 6 hours sleep), finishing off acidity issues and in these years it has also reduced my body puffiness and my weight as well. Problem is that I had to keep taking this every couple of months. Now I am not taking it as I am not sure this is the right thing. I have a habit of biting my nails (probably the culprit in the first place). How should I pursue the diagnosis/treatment for my irregular stomach?