Your urine could be more diluted than Friday, causing a fainter line. Your HCG may be doubling slowly as well. Test again in the morning, trying not to drink too many fluids before bed, and see if you can get a strong sample of urine in the morning. Some ladies take a while to show decent line progression.
Also, when pregnant, your cervix can become much more sensitive and spotting after sex is normal. Try not to worry!