11 Months boy speaking and sitting problem

Dear All,

I have 11 month old son.

1. He can sit only for 5-10 minutes with one hand support. He can not sit without his one hand support. Since last few days he is little trying to play with one hand same time while sitting.

2. He can not roll his body while laying on bed and can not move forward. Evenif we feel, he has very power in his hand and foot more than average child.

3. He has double uvula in his mouth or separated by space.

4. He has started speak( ba ba....aa ba ba...some time Aamma while crying but not very clear, some times  Ma ma and only once Pa Pa). He stop speaking some times any things for 3-4 days.

5. He was getting ill every week or second week for 1-2 days till 4-5 months. Now he is fine.

6. Doctor told brain size 40 and it should be 45 at this time. I am not sure what is this.

7. His hearing power is very high as average child.He can hear 100 meter away cracker blast while sleeping.

8. He has very cute smile on his face always for every known person evenif he was ill also. He lough very loudly.

9. I have also noticed, he can identify my voice as known person on mobile. He also start lugh loudly on mobile to response.Some times also feel emotional on hearing my voice.

10. He see me after 3 months(when he was about 9 months) he started smile too much and was trying to attract me. I did not reply him till 10 minute as I was totaly unkown. Later he started open his arm to take him. Then I took him, he was playing with me like known person. Evenif he do not go for unkown person.

I was feeling normal problems. But now doctor told,brain size 40 and it should be 45 at this time. I am in great tension. Any great man, please help by giving your valuable suggestions.