Stabbing pains in leg veins?

I went to the ER 4 days ago because of breathing difficulty and was given lovenox to prevent a blood clot (I had just spent 35 hours flying in the last 2 weeks). I had a spiral CT with contrast and no clot was found. Now I am getting intense stabbing leg pains, primarily in my left leg along with dizziness and a little nausea. The pain moves around from behind my knee up to my groin and follows a superficial vein that is enlarged and visible. Does anyone know what might be going on? I am planning on calling an Internist for an appt tomorrow.