Our normal sleep signaler is melatonin. This is made in the brain by converting serotonin using methyl B12 to melatonin.

Some drugs have been shown to impact melatonin in the brain.
SSRI drugs (your Celexa would be one of those) and also beta blockers used for the heart/ or blood pressure.

You can request a B12 test at the doctor's. If it is lower than 400, then you would profit by taking the methylcobalamin orally. This is not expensive. Methyl form is the active form, and is available on the net. Please see my Stickie on PN about B12. I used this B12 during my menopause and still do...it really helps with sleep quality.
Nutrition groups and the NIH recommend all people over 50 to take an oral form of B12 because it is so commonly low in the elderly. Poor sleep is also very common in the elderly!

You can also take melatonin orally at night, average dose is 1 to 3 mg and you'd probably want to try the 3mg. You take it 1 hr before retiring. Within a week, you may see improvements.
This is also not expensive, and worth a try IMO.

There are melatonin receptors in your retina of the eye. If you get up in the night and turn on lights, watch TV, read or come to the computer, those receptors will shut off your normal melatonin and screw up your sleep cycle. If you can, try to stay in the dark, and use a minimum of night lights to guide you to the bathroom. This light exposure alone can be enough to prevent you from sleeping more normally.