Dummy

Bit of a weird one... My son is 6 months old now but was born 5 weeks early. He uses a dummy to sleep and unless he's in a deep, deep sleep he will literally scream when he drops it out his mouth then as soon as it's back in his mouth, he will be back asleep and settled instantly. We use the correct size dummy yet he still hasn't almost mastered that 'latch' I guess as he drops it quite regularly and I don't know what to do. I'm exhausted. Any suggestions please welcome (He can't find it in the dark to put it back in either/can't do this anyway and I can't make room lighter otherwise he won't sleep)