reddish brown stuff in saliva after waking up?

Hi, I am a 26-year old male from India. Of late, when I am waking up after an afternoon nap post-lunch, I have saliva collected in my mouth and when I spit it out in the basin, the foamy saliva has a spot or a streak of deep red/brownish stuff in it, that looks like blood but i am not sure about it. This does not happen regularly but after every 2-3 days and of the several times it happened, only twice was in the morning after a night's sleep. All the other times, it was after the post-lunch siesta. I don't know why is this happening as i don't even smoke or drink or chew tobacco. Is it some sort of GERD? Please help as to what should I do. I had a history of deudenal erosion (mild ulcers) due to intake of NSAID's (Ecosprin) but that problem has been resolved after stopping that medication and having proton pump inhibitors like Pan-40 every morning. Also, I have a few loose gums around my lower row of incisors. But they bleed only if I brush vigorously or probe them with fingers. Haven't seen any blood from them or experienced any discomfort when trying to determine the source of the reddish brown saliva. Also, I am a chronic kidney disease patient but I'm not on dialysis nor have I got a transplant yet. I am only dependent on restricted diet and medication. I have glomerulonephritis and left renal artery stenosis and my serum creatinine is at 7-7.5 mg/dL. However my CBC, potassium, sodium and fasting blood sugar levels are all absolutely fine. I have an AV Fistula done in left forearm and I don't have any symptoms whatsoever except foamy protein urine and hypertension (140/100 mmHg). The medicines that I take are Pan-40, Nicardia-r 20, Minipress XL, Livogen, Betaloc, Nodosis and Gemcal. Kindly advice.