Cant get 4mo old to sleep..HELP ME?

i have a 4mo old baby boy who i love more than anything. he is my 2nd child so it's not like i'm clueless about kids, but i am having THEE hardest time getting him to sleep. at night, his bedtime, it's no problem..he falls asleep nursing. and occasionally during the day he will fall asleep nursing as well. otherwise, he will not sleep unless i a.drive him around or b.put him in his car seat and walk him around the room until he falls asleep. and he'll keep waking up and needing me to repeat this routine. i cant take it anymore! he's almost 20lbs already and it kills my arms and back to do this but it's the only way. ive tried the soothing motions glider, a swing, a bouncy seat, a co-sleeper....nothing works. i know i could try the "cry it out" thing..and i have a little bit....but we're currently looking for a house so we're living with my husbands parents and have 2 large rooms connected..meaning, my 2yr old is always close by and making lots of noise. what am i to do?? as soon as we move i plan on trying the "cry it out" method..but until then im at a loss. any advice would be MUCH appreciated, as im about to die of exhaustion, lol. thanks in advance!