My last normal period was may 16th 2017, then july, august and september there was spotting . but i did an ultrasound in august, only 2gastational sac?

"2gestational sac": My apologies, but I do not know what the term, "2gestational sac" means. If you are pregnant given your menstrual history, the pregnancy should be by now a beating fetal heart detected by ultrasound. The "spotting" may indicate that the pregnancy did not survive, which is a very common event. Get a quantitative serum HCG test to confirm if pregnancy is still viable.