Why am I finding it difficult to poop ?

Welcome to Healthcare Magic
Have you been having upper abdominal pain. Do you smoke to drink alcohol. Any nausea or vomiting. Since you get the feeling to defecate after eating and different colours of stool it could point to probable bleeding in the upper part of gastroenteric tract. You need to get yourself looked at by your Doctor and also get a stool test to rule out bleeding and parasites which can cause a similar picture. How is your sleep, urinary habits. Eat plenty of fresh fruits and green leafy vegetables, drink plenty of water. Avoid junk food, fatty or spicy food. Avoid smoking or drinking alcohol. Exercise daily by brisk walking for 40 minutes a day as well.

Welcome to healthcaremagic.I hope by now you must have got some basic idea about the troubles suffered by your intestines as informed by my colleague Dr.Raghu.Anyways i would like to advice some more tips with his advice.
1.Eat at regular time intervals.
2.Stop smoking and alcohol completely.
3.Do regular exercise.
4.Eat green leafy vegetables,fruits,salads,good combination of Carbs,Proteins and fats.
5.A glass of milk at breakfast.
6.Take Antacids in view of the black stools.
7.Consider consultation with a gastroenterologist in view of the green and black stools and also to confirm the cause of your strong gastro-colic reflex.
8.A stool examination is pertinent to exclude or confirm an occult/overt blood loss which could be due to intestinal bleeding or worm infestation.
Above all this try to maintain a very healthy life style as described above.Hope your queries have been answered satisfactorily.
Have a healthy life.