Yes it takes 48 -72 hours for a culture on urine jen. The 2 weeks is how long it takes for the result to be sent to the GP or for them to get round to letting you know. Do the tests go to your hospital? You could be cheeky and call labour ward or MDAU, and say that you would have called your midwife but she is away, and the GP has not received the lab test back and say it could be 2 wks. As you are having some symptoms, and are pregnant with twins, you were hoping they could quickly check the computer to see the result, (make sure they give you the bacteria that grew and what antibiotic it is sensitive to if they have it)? If it is pos you can then tell the GP verbally, they can get the nurse to verify with the lab by phone if they want to hear the result themselves.
Your midwife should work in a team not just alone, do you not have a number for the place they are based, who is covering her clinics?? These are people you could also get in touch with.
It can be confusing when you are pregnant as you pee a lot anyway. Protein by it self is often just contamination from discharge etc, so often turns out not to be infection. If there os blood or leucocytes too that tends to be more like to be a UTI, so don't worry too much.