telling my mum

Okay so i’m 14 almost 15 and i’m in grade 10 but because of moving country’s i’m like the youngest in the grade and me and my boyfriend of 10 months have had sex. i’m on the pill and everything and my mums knows that and i have talked to her about thinking of my boyfriend sexually but she doesn’t know we have had sex and honestly i wouldn’t tell her just yet because mum and i are very open about everything but every time my boyfriend and i have sex i get a uti and mum knows i keep getting them but she doesn’t know why. there is this company called uqora and they have a drink that you are meant to have after sex so you don’t get a uti and i really want to try it but it’s online and you need a credit card to get it and obviously i’m too young so i can’t get it. i am so stuck i don’t know what to do i just want to get this drink but i don’t want to tell mum i’m sexually active please someone recommend what i should do