Sorry Quail, I know you thought the bleed was long implantation bleeding, sorry you're still getting inconsistent results. why not buy lots of different brands and try them out with FMU and also try OPKs - if you're cd18 maybe you're ovulating?
Where in the uk are you? If you're in the north have you got home bargains near by? They have a 10mui test at 89p that is very good (no false negatives or evaps) and they also do a couple of other cheapy tests that you could do alongside it. Saver's chemists also do 99p for 2 tests and the 99p shop. Try a load of different ones, if you're then getting BFPs then yeay! if not, then probably best to start temping, keep doing the BD and see what happens in the next couple of weeks. xxx