What Causes Vaginal Spotting During Pregnancy?

Hi Doctor, I am 50 years old and i am 6 weeks pregnant for the first time can i eat cashew nuts, I feel nauseating and vomiting as well as right low cramp and also lower back pain. Am also having very little brownish spotting thought it is supposed to be that period of my menstrual cycle if I wasn t pregnant. The spotting was noticed two days ago for the first time then yesterday there was none but today i noticed a little spotting too. Please what do I do am little worried. Regards, Concerned Patient