HcG levels ?!?!?!?!?

hello so i had my hcg level done about 3 weeks ago and it was at zero I had a faint positive test Friday and darker faint on Saturday and by Monday it was gone.. I had blood work yesterday (wednesday) and got the results back as negative HCG level was at 2. can HCG levels go up and down or does this mean I had a chemical pregnancy?!