Should I be worried about my birth control?

Ive been taking loestrin birth control and recently had to take fluconazole for a yeast infection. It says it can decrease the effectiveness of birth control. I took it on the 22nd and had unprotected sex on the 27th . Im paranoid about getting pregnant. I dont know how long that medicine stays in your system and i dont have the money to get a plan b pilll. im really worried.