The red colored stool is something you need to at least call your vet about. This is a likely indicator of a lower bowel injury of some sort that is causing bleeding.
Its possible all the issues have been due to some sort of foreign object in the intestinal tract that has been causing injury and infection and is now causing bleeding. If you have not done an x-ray or a barium x-ray (helps show soft items a regular x-ray doesn't show) or an ultrasound it might be worth doing.
I would be concerned the weight gain might be due to fluid buildup.
The intestinal bleeding might also be a sign of a hereditary disease Von Willebrand’s disease (VWD) which is a bleeding disorder
http://www.cotondogs.com/Von%20Willebrands%20Disease.htm
And some of what you talk about could go along with tick carried diseases if you haven't tested for that already.
Normal temp for a dog is 101-102F so that seems OK.
I do think you need to get back with your vet. You may want to see if a second review of his health by a specialist in small animal internal medicine will give you more clues to his problem.
This site may help you locate a specialist
http://www.acvim.org/Specialist/Search.aspx
Hope this helps you!
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