Should I be nervous or no

I started my placebo pills last weekend, I am on birth control. I was supposed to get my period this week but instead I got very light dark brown blood like spotting only lasting like a day or two. I had sex with my boyfriend two times before my placebo week. I was on antibiotics too but we use condoms every time with me being on the pill. I’m nervous I could be pregnant but part of me is like I have been on birth control for a year and we also use condoms. I’m just nervous because of me on antibiotics... Should I buy a test?