What Causes Delayed Periods And Negative Pregnancy Test?

sure. I had facial laser procedure back jan12th. i just started my period then. It was very slow and then stopped. I have not had a period since, and it is March 20. I have taken 6 HPT, all negative. What do you think. I did have a fever after the face procedure, as it must have wiped me out. I had the fever for at least 4 days, on & off. Thx.