Very thin stools after bad constipation.

Ive always suffered from constilation due to an opiate medication i take but jus recently i had very bad constipation and whenever i felt the urge to go i would sit there and couldnt. I took some miralax at night and next day at work i felt an aching in my lower abdomen whenever i would bend down or get up from sitting i still couldnt have a bowel movement thay day and the aching stopped towards the emd of day the next night when i felt the urge to go i could tell it was right there so i put a finger in there to help the first part out after that the rest came out amd it was very large and dry in a few chunks i also noticed a bit of blood on the toilet paper amd a but in the toilet. It was very dark in color . Next day i pooped and it was again big amd dry but normal color. I also lost like 17 punds in last 2 months without trying. The following movements habe been very thin and soft. I read this can be symptoms ofcolon cancer should i get checked out by a dr.?