Well firstly it isn't a good idea to massage it until you have had tests to be sure it isn't a deep vein thrombosis.
I really would strongly advise you to see your doctor to assess it.
In the meantime if you get increased pain there are a few things you can do to test whether you are in need of immediate medical help.
Firstly check the pulse in your foot. I will explain how to find it.
Start on the top of the foot at the point where the big toe joins the second toe. Now in a straight line come back down the foot until you get half way between the toes and the front of the ankle. now with your fingers not your thumb, press around that area and you should feel a pulse. You don't need to count it, just check that it is present.
Pinch hard on your big toenail. When you release it the colour should return immediately.
Feel the back of the calf to see if it is hotter than the other leg. Take your temperature.
If the pulse isn't present or the colour doesn't return, or it is hot, or you have a high temperature, I would advise you get to A&E/ER straight away.
The probability is that it is a strained muscle, but I would not be doing my job if I didn't warn you of the possible danger signs.
I really would suggest that you get it looked at though.
I hope it gets better soon.
With very best wishes