BC and brown discharge

So backstory ... I had my period about 5 weeks ago. 2 weeks later I had surgery and stopped my BC pills because they put me on antibiotics to prevent post op infection (and antibiotics negate the effects of BC). After three days I got my period again. The surgery was 3 weeks ago and I spotted the other day and then took my BC. Now I’m having brown mucous-like discharge for the last two days. Is this old blood? Will it go away? I’m supposed to go on a date with the guy I’ve been seeing in a few days and I really don’t want to have to explain why we can’t have sex lol 😂 any advice?!