Thanks for the question.It is difficult to give an exact diagnosis based on history alone.But the fact the history is of short duration(just 2 days),presence of redness
and hardness suggest an inflammatory pathology.
Inflammation is a process by which our body responds to any foreign agent or stress
.Here,there is dilatation of blood vessels along with oozing out of fluid and cells into the surrounding tissue.The dilatation of the blood vessel produces the redness and feeling of warmth and fluid produces the swelling.It could be due to many reasons like stress,infection of hair follicle etc.
Some hot fomentation along with rest to the joint may help bring down your discomfort.
Wish you a speedy recovery.