Help i am in sheer desperation..?

usually the midwife will call me, if i miss and appointment or something.but i got my tests done on the thursday, one of which for std's sphyllis,hiv etc, and i was worried about this as i was promiscious when younger.so i didn't go in monday for the results.the midwife rescheduled me for 2 weeks time, and then the nurse calls me as i have a liver and heart test to get done.she says my results are fine apart from my magnesium levels.but they must want to give me medication for something.she ured me if i had an std the doctor would be in contact with me as soon as possible. but the ante-natal doctor wants to see me for a scan. does this sound serious...? what could be wrong??