How to tell if it's deep vein thrombosis or pulmonary embolism? what are the major differences?

Can be the same: In some patients a DVT leads to pe. In other patient they have one or the other. A DVT is a clot in the deep veins such as the legs, or veins in the pelvis with associated swelling of the legs. A pe is clot in the pulmonary artery in the lung and could be associated with chest pain, shortness of breath, passing out as well as coughing or wheezing.

Multiple : Dvt deep vein thrombus is in deep veins of arms, pelvis or legs. Rarely intra cardiac. Pulmonary embolism is a thrombus that moves from somewhere to the lungs.