Can feel vein/vessel inside inner cheek.

I can feel vein/blood vessel with tongue in lower right inner cheek, it's not visible when checked with flash light, but when i touch it using tongue or finger i can see that, and also 2 weeks back i had found a dark brownish patch in buccal mucosa, I applied kenacort for 2 weeks and it has reduced quite a lot, but complete darkness doesn't go away, i think my upper wisdom tooth is having frictional effect, please tel me why this is happening. Btw i got the brown spot examined in clinic and dentist said its a physiological pigmentation and no need to worry, now my question lies why that nerve feels swelled/prominent, whereas in left side of lower inner cheek i cant fee anything, its plain. Is this fungal infection or any bacterial infection? Btw i have attached the image of brown spot difference after 2 weeks in picture. Please help me, 1. Is that linea alba and why its dark? 2. Why that nerve can be felt and when i press its itchy somehow