Ann Marie,
Some people get pregnant but their hcg levels rise VERY slowly. I've heard of people not getting a positive test until they were a couple of months into their pregnancies. This is very rare, obviously, but a trip to your doctor for a blood test would help.
It's also possible you had an anovulatory cycle, which can cause a very late period. You would need to see your doctor for this again (they may do an ultrasound to see if there's anything at all growing, which is more diagnostic than the hcg test). If it is anovulatory, many doctors will give you meds to induce a period one your cycle has gone on for more than 45 days.
Early-pregnancy-tests.com sells cheap, but reliable OPK kits -- I think about 20 tests for $10. However, those will only help next cycle -- they wouldn't tell you what's going on now. If you're not already temping, you can buy a $10 basal body thermometer (from Target, CVS, etc.) and take your temperature at the same time every morning before you get out of bed. This will identify when you ovulate, since your temperature rises about 0.4 degrees after ovulation. So you only know after you ovulated, unlike OPKs, which tell you you're about to ovulate, but then you know #1 that you actually ovulated and #2 when to expect it next month.
I hope that helps!