4 days late!!!

Hi guys! So according to my eve I'm 4 days late which is unusual for me because I typically have normal cycles. With that being said I looked back at my cycle days for the last few months and I'm either a few days early or right on time. However I have been on the pill for the last 3 months, and my last period was light. I do take a pill that is supposed to give me fewer periods, I just don't know if I've been taking it long enough for me not to have one this month. Now of course my husband and I don't use anything else but birth control. Meaning no condoms and no pulling out. As for any symptoms Im not really having much. The most I have are my breasts feeling sore but that happens often with my birth control. I know that the only real way for me to know if I'm pregnant is to take a test, however I just need to know how much of a chance there is.