This probably sounds gross but im 16 and ive had a cold for a couple days and this morning when i was clearing my throat of phlegm it had blood in it. Should i see a doctor? What could be the causes of this? I have anxiety and now im panicing about it.
No need to panic 
A ruptured capillary is most likely nothing to worry about.
how much blood and what colour was the flegm otherwise?
Have you had any fever?
You should be seen by a doctor if your cold symptoms get worse over the next 2 days or so. But a bit of blood in mucus/flegm is usually no big deal on its own. without other symptoms.
Thanks for the reply. There wasnt a lot of blood, and i havent had a fever and my mom says its nothing to worry about as well, but ill keep an eye on my symptoms.
Your sinuses are dry. They sell saline nasal pump its a can. Its used as needed just saline. It will help moisten your sinus. A humidifier is also useful. Be sure to drink lots if water too. Nothing serious at all.