Yes, it is normal. Are you waking up to take your pain meds during the night? Are you icing and elevating? Also, what if any PT/exercises are you doing?
I find that my level of activity matters a LOT in terms of nighttime pain. My PT guy asked a lot of me on Saturday. Now it's Monday morning, and I've had 2 rough nights because of it -- this tells me I did way too much in PT.
For whatever reason, lots of us have more pain at night. Perhaps plan to take the max dose of pain meds just as you are turning in, and ice up your knees really well before you sleep. I wake up every 4-6 hours naturally with pain, and take more pain meds. You can ice in the nighttime, too . . . I just find it hard to stumble to the kitchen for more ice when so tired.
I've started a slow taper off my meds, but I will NOT be touching the nighttime doses for several weeks. Those are so important, because we need our sleep, and often the knees complain loudest at night. Best wishes to you, Pansy.