What Could Cause Delay In Periods After Taking Contraceptive With Implant?

Hi, i dont know if youll be able to help me but i just need some quick advice to help my worries. I have been on the implant for about 2 months and because i bled non-stop for the first month my doctor put me on the contraceptive pill on top of the implant. I was on the pill before and when it came to my 7 day break, it took about 4 days for the bleeding to start, then it would stop when i restarted the pill cycle. However, this is the first cycle of taking the pill on top of the implant and start taking my pill again in two days and i havent come on yet. Is it normal for this to happen, and if i dont come on my period by thursday should i be worried and take a preganancy test? Many thanks.