Hi. We can continue after this if you'd like.
This sounds like superficial thrombophlebitis, a clot in the vein, and these can sometimes become infected. It's treated with ice, elevation of the leg, and compression stockings along with ibuprofen.
While it isn't dangerous, it can be associated with deep venous thrombosis--a clot in a deep leg vein--and that can be dangerous since it can lead to a pulmonary embolus
You need to have a doctor evaluate this right away and I would get a Doppler venous study of the leg.