H.C.
First off make sure the three tests you took were not all from the same box. I purchased two pregnancy tests that both read negative and I was nearly 5 weeks pregnant when I took them! Also, definitely keep trying even if you don't get your period. Unless you "temp" to track exactly when you're ovulating you really don't know, so just go for it! There are also other tell-tale signs that you may be ovulating such as cervical mucus texture (yuck, I know, but it works!) and as I mentioned above taking your basal body temperature. A great book for when you're trying to conceive is "Taking Charge of Your Fertility". I can't recommend it enough! I was diagnosed with infertility last June and was able to become pregnant with little intervention in late August, even without a steady cycle just by reading my body.
Good luck to you!