How soon will I know if I'm pregnant?

I had unprotected sex with my boyfriend about a little over a month ago but he didn't ejaculate inside of me. (Pulled out when he felt himself getting close, finished outside of me.) My periods are fairly irregular in length but they usually occur at the end of the month. The day after the last time we had sex, I had a regular period and then about 2 weeks later I had very light bleeding that lasted about 2-3 days. Within the last week, I've been feeling constantly tired, experienced frequent nausea and get horrific dizzy spells several times a day. Along with that, I find myself having to urinate quite frequently, especially at night. (I paid attention to the clock last night when I tried to go to bed. I got up every 20 minutes for about 2 hours.) On top of that, I didn't get a regularly scheduled period, but I thought the bleeding earlier in the month was it. Now, with these symptoms, (and obsessive Googling) I'm beginning to fear it may have been implantation bleeding. Is it too soon to know?