-first thing in the morning is best
-keep to the time limit written on the pack (some say longer than others)
-some brands my second line was always feint no matter how many DPO I was thus why I went to clear blue digital once AF was due cause it comes up with the words "Pregnant" or "Not pregnant" leaving little doubt
-some people take time for the HCG to build up in there system so don't get positive HPTs for ages after AF is due
- I always get ten tonne of CM in the early stages of pregnancy so that is a good sign from my perspective.

A doctors blood test is probably the most reliable as you probably know since I think I read you were booked in to get one next Tuesday. So frustrating when they can't get you in any early isn't it.

Anyway again best of luck especially given how long you've been TTC. Hope you get that miracle BFP and manage to not have to go through IVF.