I have a hard lump that is sore on the back of my ankle right next to my achilies tendon. What could it be? I've had it for about a year and a half and its causong discomfort

Ganglion cyst? Difficult to say what it could be without seeing, but it could be a ganglion cyst. Thisis a tumor or swelling on top of a joint or the covering of a tendon. It looks like a spongy sac (cyst). Inside the cyst is a thick, sticky, clear, colorless, jellylike material. A physical exam is often needed to diagnose a ganglion cyst. See your doctor for evaluation & treatment options.
bursitis. Bursitis. This is a swelling that is an aggravation of the area due to irritation from a shoe possibly. If it is harder than that it could be something called a haglund's deformity.
Tendonosis. Could represent a degenerative tendon condition called tendonosis. The tendon becomes enlarged and swollen. The tendon is weak in this area. May need an MRI to assess further.