Yes, it may happen for your sitting position. Check under the following articles ; you might get some idea and answer as well:

http://www.ndri.com/article/exercise_tips_who_work_for_long_time_at_a_desk_or_sitting_position-253.html

http://www.ndri.com/article/sitting_for_long_periods_at_work_have_risk_of_developing_blood_clotsdeep_vein_thrombosis_dvt-261.html

If doesn’t help ,contact with your physician.