if you dont want to have a blood test, or an ultrasound or an internal there is not much more they can do, unless like you said you wait until 13-15 weeks to try and find the hb on a doppler, or you wait 8 months and see if a baby pops out. A simple blood test would be highly unlikely to cause a miscarriage, and an external ultrasound again would be highly unlikely to cause a miscarriage...even an amniocentsis only carries a miscarriage risk of 0.5%. If you really do think you are pregnant you are better off going to talk to your GP or obstetrician who can give you some answers. Yes there are people around that dont get positive HPT's and late HPT's but they usually go in and have a beta done to confirm pregancy