I take it that the 10mg is both gaba and melatonin with the 5mg being the melatonin portion.
First off, melatonin is not a "sleeping pill" in as much as it does not put you to sleep. It resets your body clock. That's why airline pilots take it and it's prescribed for older people whose bodies do not produce enough so they end up not going to sleep and/or waking too early, then nap in the middle of the afternoon because they have not had enough quality sleep. An endless vicious cycle.
Maybe put the jar aside for now and go get some 2.5mg tabs that dissolve under the tongue. Much more effective than swallowing them.
Lots of other factors can cause sleep issues. Going to bed without following a set procedure can cause sleep problems, so make a habit of brushing your teeth, showering then going to bed at a set time. Aim for 8-9 hours sleep, counting back from the time you have to get up.
Allow a bit of extra time to read for a bit, from a book, not your phone or computer. In fact, turn your phone off or put it on flight mode. Make the bedroom pitch dark and keep it cool to cold. Avoid coffee and other caffeine for at least 6 hours prior to sleep.
An orgasm is a great sleep inducer for men (not so much for women) so use that to your advantage.
If you are young (under 40) you are better off sorting out what's causing the problem instead of looking for meds. And for fucks sake, do not take sleeping pills. That's a road leading one way and it's not pretty.