For conceiving. Any chance of pregnancy?

Hi..I am 26 year old female.I am trying to conceive for 1.5 years.I had ovarian cyst near the ovary (8cm) it was removed three months back..after that my reproductive parts are normal..Now am described letrozole and progesterone.My last lmp was Dec 29..and on jan 25 am having very light bleeding ( Brown) lasts for 3 days..Is this a sign of pregnancy? Now Feb 5 i have tested urine test but it was negative...what it mean? Can u help for me? At hospital also i have tested (urine) it was negative, and took an ultrasound scan and transvaginal scan From that my doc said that having small cyst on right ovary.but she doubted that it may u become pregnancy. from bhcg only it will be confirmed said by her. may i know is there any chance of pregnancy?