Greeting to you
With most regards I am writing this letter to request to formalize my annual leave for 3 months, I wish to avail my leave from Aril 30th 2013 to July 30 2013 inclusive
The reason for this is that, I have important health matters to deal with as I have to undergo a minor operation for having a child and also I have some domestic problems that are to be sorted out and I need to return home for these 3 months.
I hope you will understand my situation and grant me this leave
I can only assume from the tone of your letter that you are expected to be extremely formal when writing such letters to your boss. In the UK, that letter would sound completely over-the-top and unnecessary. Here is how it would be written here:
"Dear Mr XXX
I wish to apply for annual leave for three months from 30/4/13 until 30/7/13 inclusive. I need this time off to deal with some personal medical issues, including a minor operation, and some personal domestic issues. Consequently, I need to return home for those three months.
Please authorise this period of annual leave. I look forward to hearing from you.
There is certainly no obligation to go any further into your personal medical matters so I would definitely omit "for having a child". The most information I might give would be to say "a minor post-natal operation".
As I say, I assume your boss will expect you to be very formal but, to me, "Dear Sir, Greeting to you, With most regards I am writing ..." is unnecessarily wordy and flowery. If you do keep that, you need to say "Greetings to you" and perhaps "It is with great respect that I write to you to request annual leave ..."
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.