3 worda 18 months

Dean only has 3 clear words and he is 18 months in few days. Actually he has spoke another 4 words but only heard him say it since he speak it for 2 days. Til now never heard them again. He should have 7 words but bec i never heard those words again i only consider 3. But he pretty much understand what i ask him to do like shoes, i heard him spoke shoes for 2 days only and ask him get/wheres ur shoes... but thats it. He recognizes lots of things and point them where it is when ask. He will have his 18 month vaccine this tuesday and will ask midwife about. But i also like to ask it here since we are all mothers. Is it something to worry about?