Line progression - worried!


I had a miscarriage a few months ago so I’m overly stressed and obsessed with taking these tests. I am 13 DPO and got first faint response on first response at 9DPO. Lines showed up at 10 DPO on my cheap strips. I have been more nervous too because I had had very very light brown spotting since 10 DPO. My other concern is that the lines don’t seem to be darkening as much as I had thought in the last couple of days (from 11 to 13 DPO). Makes me overly paranoid. It does seem like my hcg is higher NoT in FMU, for some reason. Any advice? Are there better tests out there to monitor progression? I have one more first response I was going to take tomorrow on the day of my missed period but otherwise don’t want to keep buying the expensive tests. I’m trying to prepare myself for the worst but really want this baby to stick!