I would also typically wake up between 3 and 3:30 am, and then be unable to get back to sleep. After years of trial and error, I have found the following allows me to consistently sleep from 10:30 pm to 6:30 am (or more) without any ill effects the next day:
500 mg magnesium (type doesn’t matter for me)
500 mg ksm-66 ashwagandha
300 mg gabapentin (RX)
I could perhaps do without one or another of these, but I don’t want to experiment and mess with my 8+ hours of glorious sleep every night!
Everyone is different, but this works for me. Good luck.