Viral throat infection and blood morning phlegm

Hi all,
So few weeks ago I had an infection in my respatory system that required me to take antibiotics, it wasnt anything that I hadnt had before. I trecoverd in a week but few days after, I started to feel like theres phlegm in my throat but when I cough it up, its only just white/clear phlegm, not the yellow stuff I cough up when I had the infection. After a week I went to the doctors again and he said I had a viral infection this time and should just wait. Now 2 weeks later, its gotten better but I wouldn't say its 100% as sometime I still feel like theres a bit of phlegm, but everytime I cough up is always clear/white. This morning however, to my horror, I coughed up some phlegm with blood in it. It wasn't like a drop or two but quite a bit. it reminds me of when you accdidently bite your toungh or right after you get your teeth cleaned and you spit out and find lots of blood in it. The blood did go away in the afternoon and I don't it anymore since. Last night was epseically dry in my area so I was wondering if that could be it but it seems like a lot more blood than usual. I called the docotor and he said just to wait a week and then go in if things dont improve. I dont have any fever, sore throat, caughing, or pain in my neck. I don't smoke at all and drink very rarely. Any idea what this might be? Could it just be caused by the dry air? My throat did look quite red compared to few days ago but I'm not a doctor. Any ideas would greatly help! thanks!