What Causes Irregular Periods?

Hello i have been wearing the Orthra evra Patch now for about 2 years no problems ever. Until now i had my regular period about 2 1/2 weeks ago, i stopped bleeding for about 3 days and it started right back up worse than ever, it subsudied about 3 days ago and is now back in action i have no clue what is wrong with me, is there some logical information on why this is happening? I will say i have been swimming alot more and my patch was peeling back but it went back on. Im not doing anything different that i did that year.