advice?:(

hey guys. so i am a week late for my period, i took pregnancy tests last week and all were positive. i went to the doctors to get it confirmed and they did a blood test, and it turns out my HCG levels are only at 140. Now, theyre trying to say that im supposed to be 6 weeks, because of the date of my LMP, and that my levels are way too low. but im confused because i normally have like a 36-37 day cycle, and only ovulate around the 20th which would make me like 2-3 weeks. they did an ultra sound (idk why because my levels are too low to see anything) and they saw nothing and theyre trying to say it might be ectopic meanwhile ive had no pain or spotting or anything of that sort. im just really confused! they wont give me any answers and they want me to come in to get my ovaries looked at. can someone please tell me theyre wrong?