Help .. never happened before

Lisa
Okay so, my periods are pretty regular, always between 31 to 37 days, last cycle I came on my period all was normal, then 2 days later I was having brown spotting for 3 days then I started which felt like my period all over again but just a little more intense ( with abit more cramping, leg ache and more blood !) This also lasted for 3 days. Confused by this I went to the hospital and they basically just said if it carries on come back. Fortunately it stopped the following day. Now I'm just waiting to come on again as my period is all messed up. Does anyone know what this is or what it could be. I had my fingers crossed for implantation bleeding but pretty certain it's not as I was on my period just before prior to this happening. Please comment if this has happened to you and what your outcomes were if any. Or even if it hasn't, all comments much appreciated