bloody phlegm?

hi! so where i live its very cold right now. lately i’ve been having a LOT of phlegm & post nasal drip which is clear. i’ve been seeing some bright red blood in it though. i have no fever and no other symptoms. my boyfriend has been sleeping with the AC the past few days even though we have the heat on in our house 😑. i’m wondering if it could be because it’s so dry in here? i definitely feel like it could be mold or mold in our ac or just the fact he keeps turning it on. but i took the ac down today. last night i had a dry throat but it went away. i’m hoping it’s just that. does anyone else get blood tinged phlegm that’s clear? just to be clear i’m not coughing up any blood it’s in my mucus that i try to get out from my throat if that makes sense lol. i’m thinking it could be allergies and it irritating my nose & sinuses… i don’t get blood every single time i get phlegm out from my nose & throat either it’s clear but i see blood here and there as well.