The discharge you had was probably the cervical mucus plug
which gets discharged at the onset of labor. The brownish pink bits indicate the spotting that occurs after the separation of membranes. The cramps if radiating from the back to the thighs definitely indicate the onset of true labor, (as false labor pains are quite common at this stage). I think that you should contact the concerned doctor and arrange for a checkup and admission if necessary. Good luck.