Two glucose tests during pregnancy?

Brooke
I was told since I am a bit overweight that I will need to take the glucose test at 16 weeks. When the nurse gave me the drink to take home for my next appointment, I asked if I would have to take it again at the normal time around 24 weeks and she said probably... I don't want to have to pay for this test twice when I've been researching and it seems the early 16 week test may be unnecessary since women tend to get GD if at all later in their pregnancy.
My issue is, today I took off work because I may have a stomach virus or ate something weird because I cannot keep food down. I haven't thrown up in my pregnancy at all besides today and my glucose test appointment is tomorrow and I have a feeling I may not be able to keep the drink down.
A nurse is supposed to be calling me back within the next few hours but has anyone declined the early glucose test and just taken it at the normal time?
A friend of mine is a lot heavier than me and she took her test at 24 weeks and was fine. I don't understand why I need to do it twice and I don't want to pay for it twice either when it's not necessary 
Any thoughts? Thanks !