Secondary post partum bleeding is referred to as an abnormal but fresh bleeding from the vagina within the peurperium. The peurperium refers to the period comprising of the first six weeks of your delivery. Since the bleeding occured within six weeks of delivery and its fresh associated with the passage of blood clots, there is a high chance that it is a form of secondary post partum bleeding. Can it be your menses? yes it can, but the more sinister secondary post partum bleeding and its causes need to be excluded before complications set in, by presenting to the hospital on time for a thorough examination and possible treatment. Causes of secondary post partum bleeding are infection of the lining of the womb, retained placental tissues and many others.
About your breast milk supply being low at 5 weeks, this is more as a result of inadequate stimulation of the nipples by infrequent feeding which in some instances can result in an early return of your menses. So before you conclude, see your gynaecologist to rule out any secondary cause of bleeding and to improve your milk production, look up the articles on common problems in breast feeding.
About the catheter irritating you around your labia, that is unfortunate as the irrritation is normal but within a few days to one week or two, the irritation normally stop once the injury inflicted by the catheter heals. If it is already reducing in intensity, i will advise you to wait it out, but if it is still intense and burns you as you urinte, you might want to see the doctor to rule out a urinary tract infection.