Is Warfarin Recommended Having Undergone A Uterus Removal Operation?

hello sir, My mother has undergone a uterus removal operation on 22/01/2011 & after that 2 days she had an attack of pulmonary embolism. she was shifted to fortis hospital n was discharged after that on 1/02/2011. she is undergoing treatment of warfarin. she was not given painkiller after operation (endoscopic operation).after her discharged we have started calpol 500 mg. which is suggested by doctor only. since last two days she was having little fever. now its not there n yesterday night she was havng headache n now it is stopped & her part of neck on the other side is paining .can u suggest what it is exactly & why it is happning.??