I finally finished reading the information from the link https://www.stevehoggbikefitting.com...leat-position/ Maelochs provided. It explains things very well, and now I understood why not only were my frontal feet hurt but also my lower legs felt so tired and whole body felt strenuous with the clipless pedals. It was a very hilly route I just took, and I found myself using the balls to pedal. I was not used to put stress on my toes or the balls of feet. When I used the flat pedals, my balls of feet were just slightly hanging over the edge of the pedal.

Well, this is a very educational thread. Thank you all