yeast infections are not contagious, contact with a partner may stimulate the yeast to grow too much.
Can it be possible your bf has a yeast infection and when having sex , he keeps giving it back to you?
I had that problem i had to stop using antibacterial soaps down stairs lol tmi and start using summers eve vaginal wash with ph balance and dont eat glazed donuts because they are full of yeast no soda because its full of junk everything you eat or drink has to pass through you and can cause infections if it has yeast or really sugary or acidy and also after sex make sure you go pee because just falling asleep or just cleaning yourself off dosent help it with throw off your ph balance
And even before I got pregnant I was having this problem :((