Napping

My 5 month old has been having troubles taking his naps. He was a great napper when he was younger, but now not so much. it's even harder for me to get him to nap on the weekends. He goes to daycare during the week and they can only get him to take 30 minute naps, if they are lucky a 45 minute one. My biggest issue is when I do get him to nap on the weekends he is usually sleeping on me. I desperately want to break this habit! If anyone has any suggestions please send them my way, I'm at the point where I will try anything. on a side note he sleeps great at night! I have to wake him at once so he can take medicine for his disorder but he falls back to sleep instantly after the bottle and meds. thanks for any advice!