Early period

Andrea
Hello everyone! Hope everyone is well 😊 
I started this app. On Sunday, so I'm still new to understanding how it works. Let me give you a quick background...I had an IUD in for 2 years. I just had it removed on December 11th, 2015. I have never had regular periods, so tracking for me can be difficult. While I had the IUD I did get regular periods. My first period after I had the IUD removed was January 25, 2016 and it lasted 4 days. According to the app I would be fertile from the 3rd of Feb to 9th of Feb. My next period is supposed to be on the 22 of February, but I actually just got it today the 18th of February. How can I keep track better if I'm irregular? 
I will say that a day or two after my last period I felt that slight twinge on one of my sides as if I was ovulating. Could it be possible to ovulate so soon after my period? 
I feel a little stressed with all this. And a little part of me wants to not keep track and just try. My sister never kept track and got pregnant with all three of hers with no problem the first time around each time.....maybe I can be as lucky.  
Thanks for any input 🤗🤗🤗