Brand new pregnancy or chemical? low beta

Gaelyn • Rainbow baby Stevie Grace born Feb ‘18 after 3 losses. TTC number 2. Wife of Chris. Stepmom of Zoe (13) Pitbull mom. Lover of rainbows, sunsets, summer, adventure.
I have just found out I'm pregnant! It's my 4th pregnancy after 3 miscarriages so obviously terrifying. It's made even more complicated by the fact that I had major surgery on my leg and foot a month ago and have been on hectic meds. (We were using Glow to track ovulation and took 10 days off during my fertile window, so don't know how this happened!) AF is 5 days late, and a HPK showed a verrry faint line (not my FMU.) So because I'm on serious meds I went to get bloods done asap and my beta is only 20, which means either a pregnancy that won't stick or I'm literally just a few days pregnant! Dr wants me to start on Clexane, progesterone and a specific folic acid tonight. And I must redo the beta after 48 hours on Saturday. She will only get those results on Monday though. Argh a whole weekend of waiting! So it's possible this is a chemical pregnancy, where the pregnancy is not going to stick and that's why the levels are low. Or it's just that I ovulated late and this it's just super new. I also have to stop the pain meds which terrifies me as I'm still in a LOT of pain every day. 
​Does anyone have experience of a super low beta - did it turn out to be a chemical? Or did you just test really early on and that's why it's low? I don't want to get my hopes up for nothing so any input is much appreciated!