Should I tell him?

So my ex and I had sex on 12/10 and 12/23. I started the birth control shot on 12/12 and we used a condom on the 10th. On 12/23 we had sex twice without a condom but I used plan B. I'm now 5 days (projected on the 24th) late and I'm not sure if I should tell him because it could be my birth control shot or the plan B delaying my period, and we ended things on a bad note. So what I'm asking is, would you tell him or should I wait? And if I don't wait, how long until I should say something?