Period tracker

I got my period on the 3/4th last monh. It lasted until the 9th. And on my period tracker it says im due my next one on the 17th. Is this correct?
 I havent had regular periods for years, and atm im on the implant from march and didn't get a period until last month. 
Shud i get them reguarly now? My boobs have also started to get a bit tender if thats anything to go by!