Help-first response! Early pregnancy

Hi, I was wondering whether anyone would be able to offer me a bit of advise about early pregnancy detection. I have recently gone through an ectopic pregnancy resulting in me having emergency surgery to remove my right Fallopian tube. This was done in October. Me and my husband celebrated our first wedding anniversary last week and it coincided with me ovulating. This may have been a very foolish thing for us to do considering but naturally we ended up having sex (several times 🙈🙊😍) today I have started to have abdominal pain on my left hand side. This could be absolutely nothing, but I can’t get the worrying thoughts out of my mind. It’s really important for me to detect pregnancy early so that if an ectopic were to happen again, it could be potentially flushed out with medication rather than surgery. I really don’t want this to happen as I want our chances of conceiving naturally to still be an option (where possible)

I was wondering whether anyone was able to offer any advice on whether they had success with early pregnancy tests such as first response? My period is due on the 21st so according to the details it’s still too early to test at this stage, but I just want to know whether it’s worth me getting as prepared as possible if these tests are any good.

I would appreciate any advice/words or wisdom.

Thanks for reading-a very worried TTC woman. X