Hi Nicola
BF i conceived i stopped using OPK's never got a positive. Don't let that hold you back, just bd as normal or more than normal

I had a lapscope and was very fertile after the surgery, unfortunately it ended in a MC. We TTC for a couple of years and eventually got it right. Don't stress that you are not getting a smiley face, maybe try a cheaper brand (or the brand that you used before these)
Are you tracking your temp? That helped me a lot, it is tricky in the beginning but it helps you to get a better idea of when you are ovulating and when AF is coming. I used 2 thermometers one orally and one vaginally and just used a normal excel sheet to catch the data and to compare. But you can download Fertility Fried, really helpful app.