maybe you could have an iron deficiency or really low blood pressure, both are known to make you feel drowsy and tired, as well as hidden allergies you may have not noticed. i think it ain't fair not to run a blood test, and, excuse my french but it's a complete bullshit to say that if urine doesn't pick it up, blood won't either.
your doc needs to revisit her biochemistry lessons, blood test is a quantitative one, up to 10 times more sensitive than the urine one (can detect below 1 unit per ml, compared to 12-25 units, which is the usual EARLY DETECTION urine test sensitivity limit. cheap ones are usually around 50 units cut off...).
plus, blood concentrations of HCG are higher than the urine ones and NOT affected by how much water you drink (and if you drink a lot, it can dilute the hormone below detection limit in the early stages of pregnancy).
try another doctor perhaps?