I Am 70 Yrs Old. Had Problems With Severe Irregularity

I am 70 yrs old. Had problems with severe irregularity had a colnoscopy 6 mos ago, my third on ten yrs. No polyps found. I have had a twisted colon but not a concern from GI. I am taking Amitiza, very expensive but I have tried many. It worked and I seemed back on schedule and stopped and started up again but now isn't helping. I have not had a bm for 5 days so have taken a bottle of magnesium citrate. Doing its thing and some relief. No pain just have felt awful for a week.
I watch what I eat, drink 2-3 glasses of water daily. Should I be concerned of blockage or other issue?