Hey, I'm sorry you're going through this, it sounds similar to my miscarriage last summer. I was classed as pregnant of unknown location as they couldn't see anything but my hcg, although low, was rising slowly. I was at risk of an ectopic anyway so was closely monitored. I absolutely didn't want the methotrexate injection and I was fortunate enough that my levels did then drop and I miscarried naturally. I was managed conservatively as my levels were so low and they couldn't find anything so if your levels remain low and they still can't see anything in your tube ask for more time before the methotrexate - as long as they can't see anything growing in your tube that could rupture obviously. Also, the information I received was to abstain from ttc for three months for every infection you have so if you only have one it would be 3 months, if a further injection is needed its 6 months and so on.
As hideous and heartbreaking as it is I hope you miscarry naturally and your levels drop so you don't have to face anymore trauma. Lots of love xx