I'm experiencing mild abdominal pain some times, sometimes in lower abdomen other times in upper(worsened by after meal), constipation & bloody stool.

Need to examine: Blood stools warrant an examination by a doctor. It is not feasible to provide a meaningful opinion without examining you. It may just be hemorrhoids, however, even that needs to be treated. It would be prudent to see your doctor. For good health - Have a diet rich in fresh vegetables, fruits, whole grains, milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Drink enough water daily, so that your urine is mostly colorless. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco, alcohol, weed or street drugs in any form. Practice safe sex, if you have sex. Get HPV vaccine