What Could Be Causing My 3 Week Shortness Of Breath, Muscle Fatigue, And Nausea, Given An Elevated D-dimer Level?

Hello, please advise. I am a 35 year old woman and I have recent shortness of breath for almost 3 weeks(sporadically throughout the day) my muscles feel tired(burning sensation) with some activity. Also have nausea and upset stomach occasionally over the 3 weeks. Chest X-ray and ct scan as well as Blood test for wbc and RBc normal except elevated d-dimer (357).