What Causes Soreness And Swelling In Calf?

After travelling to Malta from the Uk on 24rd December, I found my left calf was sore & slightly swollen. I could see a slight discolouration which is now purple. Yesterday I my the top of my leg felt sore and I have a slight swelling with discolouration. Should I be concerned? I have not had any accidents for these bruises to occur.