I don't know exactly why the doctor wouldn't see it. One thing is I suspect the colon cleansing you do before the colonoscopy flushes out the obvious signs such as tapeworms in your gut. Many of the parasite eggs are tiny and invisible. Not sure how visible a tapeworm head attached to the intestine is. I believe flukes tend to live in other areas.
The other problem is that doctors in the US tend to think of parasites as a 3rd world problem. You don't find what you don't look for or know how to look for.
The funny thing is that we worm our pets and livestock regularly in the US and somehow assume that people don't need to do the same.
The bottom line on all that, however, is you are the master of your body and know it better than anyone else. A single dose of Ivermectin or Pyrantel will give you good idea... as well as you will know when you feel good. Based on your photos, flukes seems likely. You could try to confirm with an Elisa test, but it's probably easier and cheaper to try a treatment.
As far as sources, it's wise not to post them on the forum because authorities have been cracking down.
I am currently in Thailand and not up on the current sources in the US. Most people in the US seem to use online veterinarty sources; many of the animal meds are the same as for humans... not always the case, but I've heard of people successfully using albendazole for cattle, ivermectin and pyrantel for horses, praziquantel and pyrantel for aquarium use. If you live in a rural area, you may be able to find some of these things locally at a feed/aquarium/pet store. You do need to read the labels carefully to make sure it's the correct active ingredient and there are no additives, and it's wise to use only what people have reported using successfully. In the past, I've used what I mention above.