My sons girlfriend is living with us. now some of my pain meds and sleeping pills have disappeared.what now?

Be responsible: Pain medications and sleeping medications are controlled substances and require a high level of responsiblility. When you expose those medications, others may take advantage of you. It is up to you to keep them in a safe place and out of sight. The issue of your son's girlfriend living with you is an issue your apparently have accepted. With the above, you will have to deal with it asw it is.

Lock them up: I have my patient's put their medications in a locked box on top of the dresser in their bedroom. That way the only access to it is with a key. If the box is broken into or disappears you will know right away. Hiding your meds is not a good idea as they will be found and you will drive yourself crazy trying to remember the last place you put them.