My ultrasound report said '' no mass or fluid seen in uterus and normal in size " , i had sex 4 months ago. can i be pregnant?

A urine : pregnancy test detects B-HCG in the urine, which is present during pregnancy. A negative urine pregnancy test 4 months after sex certainly rules out a current pregnancy. There is nothing in your ultrasound report to suggest an intrauterine pregnancy. Early pregnancy (less than 5 weeks) will often not be seen on ultrasound however. The answer to your question will be found with the test.