Dulu,

I'm sorry you are feeling fear of the unknown. Fear is much easier to deal with when you know what you are dealing with. I wish that fear wouldn't keep so many people from investigating what they are scared of.
If you become aware of changes in your body that cause concern, contact your doctor right away and explain your concerns. Your PCP believes your concerns are valid and sent you to a gastronoligist.
I would contact your PCP and ask to have their office call and have your Colonoscopy moved up over concerns of a blockage. Two months is too long wait.
Also ask your PCP to write a script for blood work right away. Ask for basic blood panels like a comprehensive metabolic and a CBC as well as CEA & CA 19-9. The last two are important as they are cancer markers for Colorectal Cancer. They are not sure signs, but can relieve some worry, if they come back normal, until you get your colonoscopy.
I'm not a professional, but have gone through a full bowel blockage with emergency surgery, that I had clear signs there was a something wrong months before I was forced to address it.
I could have started treatments much earlier and avoided a host of issues over the last 4 years.
Like all cancer concerns, early detection is the best way to attack it and the improvements in treatments are near miraculous now.
Do not beat yourself up over not acting sooner, you have acted now and are on the way to any recovery required. At a minimum you can ease your fears and know you have started on your path of celebrating many more upcoming Birthdays.
Happy 73rd birthday and the many more God intends to give you !!