hey K.,
it sounds like your little baby has started to grow up, something all us mothers dont want to happen. i have 3 kids and they all did the same thing at that age. they have a sense of independance and want to do things when they want to do them. here are a few suggestions for you that worked for me.
1. give him a bath in lavendar scented bubble bath, it soothes them and somehow makes them really sleepy. have no idea why but it works.
2. try laying with him in your bed or on the couch. once he is good and asleep put him in his bed or leave him there and just make sure he will not fall off. if he doesnt fall asleep after 30 to 45 minutes let him get up and play and try again a few hours later.
3 also make sure he has a full belly, babies seem to go to sleep faster after they eat.
4. take him to a park or outside to play and get him really tired out.
5.take him for a car ride most babies fall asleep on the move.
6 if nothing else works then just let him fall asleep by himself when he is ready.
i hope some or all of these work for you. keep in mind babies dont stay predictable forever. keep in touch and let me know if i have helped in anyway. J.