If I have been cleared of DVT via 3 ultrasounds and a negative d dimer. Is it possible to still have a pulmonary embolism?

Unlikely. Negative d- dimer is very predictive that no unusual clotting is happening.
Probably not. If you have any chest symptoms a ct of the lungs rules out that possibility. So with the tests you already had it appears to me that any blood clot has been ruled out in the lower extremities.