Dr Browns bottle

Hello ladies my son was born a preemie born July he was due Sept. the hospital gave me 3 bottles when he graduated to come home after 41 days in the NICU . The bottles they gave me are the same bottles he used there . Lately the bottles keep dripping what is it that I’m doing wrong ??? I’m so frustrated with these stupid bottles . They’re for preemie babies . He will be 2 months on Monday his last weight was 5lbs 10oz idk if I can change his bottle now.