30 weeks pregnant

I was up in hospital on Friday because i had some cramping, back pain & i felt alof of pressure in my vagina, they said everything was fine and did 2 swabs because i had some discharge, they told me if they dont call within 2 days it means everything is normal, so today i have not got a call from them so im guessing everything is fine but few hours ago i started having some burning in ma vagina and its not only when i have a wee its there when im sitting or lying down, could this mean i have an infection even though hospital did tests on me and everything came back fine? The burning isnt too bad but i can feel abit & im getting abit worried, I have also started new tablets yesterday because it turns out i have anemia and i need to take iron tablets, don't know what might be causing this burning sensation