My son is 3 months old and will only fall asleep when I rock him. I then put him in his cot but always wakes I?

 I love rocking my son to sleep but when I lay him diwn he will wake in 10minutes. Everyone says I have to let him cry to learn to fall asleep on his own. I feel he is too young am I wrong? He also sometimes sleeps with me to get a good nights sleep last night by sleeping with me he slept 11pm to 6am. Do I keep doing what I'm doing or do I need to change?