Why do doctors want me to be on blood thinners for two or three months after being cardioverted?

Prevent stroke: I presume you had atrial fibrillation or flutter. If this is the case, a minimum of one month of anticoagulation ( blood thinning) is critical. When you are in these rhythms, your atria are not contracting and it might take a week or two before they start, in the meantime, a clot can still form and then travel to your brain (stroke). Anticoagulation after one month depends on many other factors