Hello. I'm 21 Weeks Pregnant And Over The Past Couple

Hello. I'm 21 weeks pregnant and over the past couple weeks I keep needing to clear my throat. I was prescribed antibiotics at the beginning of this week due to what I thought was a sinus infection. But this morning when I cleared my throat, I had some bright bits of blood. Is this serious? Where could it be coming from? Was maybe thinking it would be from my nose but it trickled it's way down my throat, sometimes when I blow my nose I have bits of blood. I'm very worried, I have convinced myself it's a sign of a type of cancer, but two weeks ago I had a chest X-ray and everything was fine?