What Causes Blood In Sputum?

Question : Hi Doctor, I have an issue which I am very worried about. About 2 weeks ago I noticed blood when I spit, mixed with salivia. I went to a&e. The doctor examined me in terms of making me open my mouth, say ahhh and putting a light to check in my mouth and throat. I have no cough but I am a smoker. When I do cough and bring up mucus, there is no blood. It happens when I gather it up in my mouth and spit out. There is traces of blood (pink coloured as mixed with salivia) This has been going on for 2 weeks now. Its worse at night. I went to see my gp who did the same tests and again said its nothing to worry about. The first doctor said its coming from the throat and isn't the bad type of blood although it feels like its coming from my mouth and not inside. Just over a week ago I went to the dentist who cleaned my teeth and removed my wisdom tooth. There was a lot of bleeding after this. (I went dentist after I saw blood in my salivia). This has all healed now but the traces of blood are still there, still the same and agaion happen a little more at night. Seems to happen when my head is up but this may just be in my mind. Its seems like its coming from my mouth as when I gather it and spit, blood comes out but there are no cust or sores in my mouth although gums are a little red. When I put a tissue in my mouth, no traces of blood are there. Could this be coming from the salivary glands themselves and if so, could this be a serious illness? It seems to gather more from the left side on my mouth. My ear seems to be blocked for a few seconds in the morning but this has been happening for months and I am not sure if its related.