What other tests should I take to find the cause of intermenstrual bleeding if Pap Smear and Ovarian Tumour Marker results are negative?

I would recommend a review by a gynaecologist or a GP to review a full medical history as well as menstrual history and physical examination. From history, physical examination and the profile of the patient, doctors can narrow down the causes and prescribe diagnostics tests as required. For example, in some patients I may recommend a US of the pelvis or even hormonal profile to further evaluate for other causes of intermenstrual bleeding.