I had very hot burning sensation when i pass stool. i am having constipation also and its semi liquid and very less in amount. i had spicey food last.

Hot food to blame: Almost everyone has had that experience after eating unusual or spicy foods. It is typically self-limited and passes after a day or two. This would usually be associated with loose stool (I'm confused by you saying you are constipated and have semi-liquid stool). If burning persists, or you have rectal bleeding or mucus you should seek medical attention as this could be early proctitis/colitis.