As to whether the boyfriend using meth can somehow be transmitted to the infant before birth: Sorry, this cannot happen. Nor will taking Claritan D cause the newborn to test positive for meth. Pseudoepinephrin is transmitted to the baby in breast milk, but the American Academy of Pediatrics doesn't necessarily see a problem with this.
I don't practice this kind of law, but given the facts in the question, if I did, I'd have to ask you to consult a different attorney. Sorry.