Hi,please answer the following questions:-

1. wht is difference between :-
i think ---and ---i do think


2. is there any grammatical error in the following message:-

hi andy,
david messaged you regarding john in the morning, but you haven't reply to it.is there everything fine? and i'm extremely sorry if i'm disturbing u and if david was disturbed you.
bye

3. can we use were in conditional sentences .


and 4. suggest any good website to post articles , so that they can check my grammatical errors..

thanks in advance-----bye