I think you should get a doctor to check this out, as swollen and tender calves could be caused a number of conditions... making it very hard to try and diagnose the problem without seeing you.
My main concern is something called DVT (Deep Vein Thrombosis), which really does need to be examined right away.
It could also be a spider bite: Do you think you might have come into contact with a spider that could have caused this? Are there any bite marks on your leg?
The swelling and warmth that you describe can be a sign of infection, which is what leads me to believe it could be a bite. Insect bites often cause bacterial infection if left uncleaned. The saliva of certain insects also causes a reaction which can be very uncomfortable (mosquito bites are notorious for this).
If this calf problem persists, please don't ignore it, get checked by your doctor!
Or if you don't have one, go to a walk in centre or an ER department.
I hope you feel better very soon.