What Causes Periods Twice In A Month?

Hi I went to the doctor about 4 months ago and told them that out of the blue my periods started changing and it s been going on for about 6 months they said back then that it was just hormones but I m really starting to question if it s something else cause why is this still going on. Okay so anyway my period was always regular before November, it would come on the 28th of every month but when November came it came three days early, then in December it came 5 days early then January it came 8 days early, then February it came 11 days early, then March it came 13 days early, then in April it came 15 days early, And now it s May and it s 18 days early. I m so concerned and confused now because why did this just all the sudden occur. I ts scary and I think there s something wrong with my body I don t thank it s the cause of hormones. I ve had a period twice in a month so I really don t know what s happening.