How probable is it for me, 30m, relatively healthy to have a blood clot in my calf? (dvt). and if it is dvt, will it go away or do i need a doctor?

Depends: You would be at high risk if you recently traveled and were immobile for a period of time or if there is a family history of clotting disorders or blood clots. If you have significant swelling in 1leg and pain in the calf then it should be checked.

Dvt: Depends but in order to make itself feel more comfortable venous duplex ultrasound (Doppler-sonography) would make the diagnosis or rule out that diagnosis. Antecedent factors could be vigorous physical activity, or recent airplane travel.