What Causes Frequent Urination, Nausea And Sore Breasts?

My last period started on the 17th of December and ended on the 21st of December 2010.For the past couple of weeks I have been experiencing a range on symptoms - frequent urination, nausea, sore breasts, tiredness and feeling extremely emotional.I took a pregnancy test on the 14th of January in the morning which resulted in a faint positive. The next a negative and the third a faint positive. However every test after that has been negative. I must say that I have not tested in the morning at all times and some samples have looked very weak.I am fearing that I have had a chemical pregnancy although I still 'feel pregnant' and I haven't bled.This is really starting to frustrate me as you can imagine. I just want to know..Am I pregnant or not?