Try waking up at different times. For example, I wake up at 2:30 AM, I can't go to sleep. I wake up at 3:30 AM, I can't wait to go back to sleep. I guess you try to time it where you don't wake up right after a deep sleep stage. Just my guess. But do try waking up at different times.

If insomnia still plagues you, try doing other stuff before bed. You don't necessarily have to wake up in the middle of the night.

And don't give up. I've been trying to induce a lucid for the last 30-something days. But I haven't given up, and I won't until my curiosity is purged.