What Causes Delayed Periods While On Contraceptive Pills?

Hello. I had sex last night, but he did not wear a condom. I have been taking Junel, the generic form of Loestrin for a while now. I took it for several month, but then was off it for about a week. I resumed taking it 2 and a half weeks ago. He pulled out before he ejaculated. But my mind is not at ease, especially considering that I don't think this guy is ever going to talk to me again. I am 32 and should know better. I wish we had used a condom, but what's done is done. I am very scared and I don't know what to do. Money is extremely tight right now, as I cannot even afford the $50 for Plan B, let alone an abortion, if I do, in fact, turn out to be pregnant. I know that the pill is 97 % effective, but should I take a chance on not using any emergency contraceptive before it's too late to do so? I don't know what to do. Oh, one other thing: I do not have periods, partly because of the pill and, also, because I am a little underweight. Therefore, I do not know how to keep track of my cycle in order to tell if I may or may not be pregnant. Please help me.