I Suffer From Constipation But Recently It Became Worse I

I suffer from constipation but recently it became worse I thought it may have been due to taking antihistamine for 2 months. I take citalopram 20mg also. Unfortunately my bloods have show hb 10.5. I am 56 years old.since taking a few doses of movicol I have been ok. I am due to have a virtual colonoscope.
Do u think the anemia can be due to the medication