What Causes Vaginal Bleeding During Intercourse While On Mirena Coil?

Hello i have mirena. Over 2 yrs .now this isnt the first time ive had mirena no issues last time. All of dec i spotted. Stop n start it was annoying i stopped dec 29th had sex dec 31 n in the middle i started bleeding only during sex that was a first... Week later i had cramps n a headache so i went to my dr the other say they did an internal n external ultrasound n there was alot of fluid in there dr said infection so im on 2 dif antibiotics but my question to u is could there had been any possible way i am pregnant n would they had saw it on the ultrasound?