Complicated pregnancy

Hi all, am sharing with u my experience to check if anyone else did came across such thing as well. I am supposed to be 7 weeks pregnant based on my first day of last period which was on 30th October. I went to KKH last week and nothing could be found both in ultrasound and vaginal scan. Took blood test to check HCG level however it has been decreasing slowly from 822 to 695 for my past 3 visits to KKH. They suspect it might be ectopic pregnancy but nothing could still be found. My ovary, uterus and womb are perfectly good and I'm normal. No bleeding or pain as well. Doctor suggested I could take the MTX injection to kill the pregnancy blood cells but we choose to wait 2 more weeks to check my blood and do a scan as well. Anyone else going through such similar issue. Do let me know and share with me what could be the reason. Thanking you in advance