Sleep problems

Rachael

So my DS is almost 8 months old. He used to be a great sleeper but as time has gone on has started to refuse nap time even when tired and only sleeps for 30 mintues before waking up. I've tried putting him down before he's tired and even tried stretching out time before his naps. Sometimes he goes almost 4 to 5 hours without wanting to nap and if he does again it is only 30 minutes and wakes up rubbing his eyes seemingly still tired. Sometimes I can coax him back to sleep though rarely. He doesn't sleep through the night without waking up at least twice either. I'm concerned about how much sleep he clock's because the average is meant to be 14 hours but he is lucky to get 12. Am I meant to get him to go back to bed after 30 minutes or just get him up even though he hasn't slept enough?