Were you on oral contraception? That is what caused my DVT in my knee 2 years ago when I was 38. Since I was on the oral contraceptives to suppress my periods due to Stage IV Endometriosis, I was immediate switched to Depo Provera and put on Warfarin. It's certainly worked so far for me, but obviously my diet had to change.
I'm just saying that it could be due to oral contraceptives, obesity or lack of activity, since all three are risk factors, even at a relatively young age like in your case. Just some food for thought.
Camp Good Grief 5k 2012 - 31:50
Gobble Wobble 5k 2012 - 30:00
Turkey Trot 4 Mile Race 2012 - 38:38
Ugly Sweater 5k Fun Run 2012 - 27:19
Move-It Memphis 10K 2013 - 55:36
Germantown Half Marathon - 2:08:53
FedEx St. Jude Classic Fairway 5k - 4/13/2013
Pittsburgh Half-Marathon - 5/5/2013