How can i tell if the cramping muscle pain i feel only in my right leg is a dvt? started suddenly, lasting 3+hours.

It is constant drag: Dvt usually causes dull pain and swelling, especially after long travel or rest or injury. if cramps and swelling, get venous doppler, but in ur case looks normal.

DVT diagnosis.: The gold standard test to evaluate DVT between the groin and mid calf is a venous duplex ultrasound. The accuracy of this test is well over 90%. A d-dimer blood test is also a good screening test if negative but it can be positive for many reasons besides DVT.