Can your 11 month old say any words yet?

does your 11 month old say any words yet? my son is 11 months old in less than 2 weeks and all he can say is dada and not that often, he will say it a couple of times 1 day and then not say it again until weeks later he has said mama but only a few times he hardly babbles just blows raspberries all the time and screams ( not crying screaming just random screaming noises) is this anything to be concerned about? he started sitting up 1 day before he turned 9 months old and started crawling about 3 weeks ago but not on his knees he just uses his arms and feet to drag him self round the room. so he is pretty slow with stuff also he is very strong on his legs but when i stand him up on his feet i hold onto his hands and try to get him to take steps but he doesn't no how to put 1 foot in front of the other shouldn't he know how to do that by now as well? he can lift himself from sitting position to standing while holding my hands to pull himself up but cant yet sit himself up from lien down thanks for your help.