Had robotic hysterectomy 3 weeks ago now seeing a little bloodi n stool what do I do?

Blood in stool. Post operative complications. These regretfully do happen may be nothing but call your doctor. Your doctor can evaluate and most certainly will want to know.
Relax. A bit of blood can pass from the vagina for several weeks after a hysterectomy. That is the most likely thing going on for you now. You should be seeing your doctor for an exam at 4 to 6 weeks after the surgery and if there is a problem it will be found and treated. However, if you are worried or if you have excessive bleeding you should see your doctor right away.