I Started My Period Three Days Early In December, It

I started my period three days early in December, it was irregular, very light and only lasted for 3 and a half days. It is usually very consistent for 5 days. I went to the doctor, they took a urine sample and said that I had a bladder infection. I took the medication as prescribed, but my period is on 3 days early again and very light again. I am very concerned.