You should keep on taking your antibiotics. Once you are on the 3rd trimester, lumiliit na yung space na ginagalawan ni baby and you can't expect them to be very active all the time. As long as you can have 10 movements within 2 hours in a day, baby is fine. The antibiotic you were given is perfectly safe. Pag hindi po na treat yung infection nyo, there is a possibility of transferring the infection to your baby and you will have preterm delivery. Make sure to drink plenty of water and take your medicine with full stomach. Inform your OB right away for any changes in the pattern of your baby's movement.