Rectal bleeding. Ailment. please help!

I have been having rectal bleeding. Bright red colour stool passed drop wise and after passing stool and some of blood covering stool .It has happened twice in 2 months. First time I had constipation and I passed hard stool and blood came out with it drop wise after passing stool. While passing stool it is painful otherwise I do not feel any pain. I visited a gastroenterologist and he gave me medicines of hemmoroids and isabgol powder. After one week I stopped passing stool. After about two months I stopped taking isabgol powder and again passed hard stool and it again started bleeding. This time amount of blood was less and also some blood covered on stool. It has been 5 days but small amount of bool is passing along with stool. I have again started taking isabgol powder. Is there a need to go for colonoscopy or it is just hemmoroids and will cure by itself . Is there any risk of other ailment. Please help