You should not be concerned about the
colonoscopy next week, which although it is an invasive procedure, it has low risk of complications (serious complications less than 1%), however you should know which they are. Serious complications of the procedure including bleeding (particularly after a
polypectomy), cardiac or respiratory problems due to the
anesthesia, and perforation of the colon (which could require surgical repair). These are rare but can happen. The good thing about a colonoscopy is that the doctor can directly look at the whole colon, including the
terminal ileum, which is in the area you may be having problems. If there is a large polyp causing problems it can be removed immediately, and if there is inflammation or an ulcer, biopsies can be taken to rule out a cancer. The fact that you have been losing weight, you are constipated, and you have right lower
abdominal pain is concerning for a problem in that ileum/
cecum area. If you desire to have a non-invasive test, talk to your doctor, since other diagnostic tools are available such as a
CT scan of the abdomen with contrast. You can also check with your doctor if they have available at your local hospital a "Virtual CT colonoscopy", which although it is not the panacea, it is a non-invasive procedure (you still have to take the laxative preparation the day before the test).
Hope that helps, let me know if you have any other concerns.