I used to be just like that! I would long for a nap but it would take a while and then I’d get hardly any sleep at all. What helped me was practice, on days when napping was an option I would have a quick coffee, (otherwise I wake up groggy)lie down or stretch over the table at work and close my eyes. Sometimes I wouldn’t sleep, but I’d have ten minutes of relaxation at least. It didn’t take too long and now I can be just about anywhere and fall asleep if I know it’s potentially naptime. Having a pre-nap ritual (coffee, setting alarm) really helps tell my brain it’s time. Maybe that can help you!