Sometimes the cause can be related to medicine, such as birth control pills.
And, sometimes it can be related to another, underlying
and perhaps quiet
and undiagnosed, medical condition.
This is no time for any uncertainty regarding the cause of the clot or its optimum treatment. If your doctor is uncomfortable with or resistant to any of this, you should request a second opinion with a doctor experienced in the management of deep vein thrombosis and thrombo-embolism.