You can track you ovuation and make a chart like i did! It put my mind at ease and I was able to not stress DH (dear hubs) for BD (baby dance) coz we are both working. You can get the ovulation strips online, they are really cheap for testing alot or you can get the clearblue ones which are more expensive but it works for me too. I was able to track when my period comes after my ovulation has ended and track my lutheal phase.
Perhaps you can try TCM to regulate your body clock or go to a gynae to check if everything is ok. Seek help early!
Does it mean your menses comes every month but sometimes early and late?
Have you tried the ovulating stick?