Generally the doctor's tests will be less sensitive than the shop ones, so there is a good chance you are pregnant.

The reason they say a BT is inconclusive is if you have HCG (pregnancy hormone) in your system but only a low level so not sufficient for them to say yes you are pregnant. As the others have said, it could be one of two things.... Either the BT was taken before there was sufficient HCG in your system and a repeat test will show more & give you a positive result. Or it is a chemical pregnancy. This means that the egg was fertilised but failed to implant correctly.

Even if you test daily the lines may not get any darker, as long as there is still a second line it's a good indicator. If the line dsappears completely (given you use the same brand each time) then you are more than likely having a chemical pregnancy.