I don't think that you were as healthy as you thought you were or at least you never noticed it! After what you say I think that you had a chronic infection of your stomach which also affects your transverse colon and the SBO triggered break up of the biofilm in the transverse colon. This has not healed and without their biofilm partially protecting the colon it was exposed to enzymes which caused bleeding.
You could try a deep enema to clear the colon back as far as the transverse colon and then introduce probiotic bacteria such as Bifido bacteria into the colon via enema to see if they resolve the situation. Hopefully they can destroy any infection that still remains. Hold it in your colon for as long as possible. You could also add nutrients for colon health such as glutamine, inulin for butyric acid production and possible some d-limonene. Making a liposomal form of d-limonene with lecithin might be helpful as the oil will not mix well in water without it and the oil will probably float on the enema water and not enter the colon.
In addition there are some amino acids which can stimulate healing of the digestive mucosa but getting them might be difficult. Some are fairly easily available but others I have not had luck finding. Threonine is easily available, Proline is available, Cysteine is harder to find but N-Acetyle-Cysteine is easily available although I am not certain that it is so easily used for the purpose intended. It is meant to be more easily absorbed but whether the colon/digestive system can use it I do not know. The really difficult one is Serine which I have not been able to find, other Serine complexes are available but not pure Serine. This is one I a missing ATM. The others, in the forms that I mentioned I do have.
D-Limonene is meant to help heal the digestive system and is why I purchased some. It is also meant to have some anti cancer effects, particularly on cancer cell metastasis. D-Limonene is an essential oil from the peel of oranges and similar fruit. Food grade D-Limonene can be purchased fairly inexpensively.