Could i have a blood clot?

after having my son 7month ago i got a pain at the back of my leg (back of knee) after doing some walking after i had sat down and rest for about 10 mins then when standing back up again i got a pain and like a cramp and had to slowly move my leg till the pain went.. i then went to the doctors is werent swollen or anything like that but hurt after any walking. the doctor werent concerned as there was no other symptoms.. i signed up at the gym and it went.. since i havent been going to the gym for a few months and just sitting about the house with my son any walking yet again and its back pain in the back of my leg and when i stand it isnt warm to touch but my leg feels warm in the area that hurts.. could this be because of lack of exercise of could it be a DVT?