4 days have passed since I arrived in the Philippines.

It seems that I have caught a cold in the plane, because the air conditioner was too cold.

So today I didn't go to the lessons and laid in the bed.

I was surprised that, It was extremely big, huge. (you can use huge too, but use only 1 word)

I bought some beers (I love beer!) and water melon and mangoes there.

It was only cost less than $10. (It was less than $10 is also ok)

Mangoes are also much cheaper than in Japan.

You can buy more than 10 mangoes in the Philippines for the cost of 1 mango in Japan.

I Have Caught a Cold.Comment: As this is the title, initial capital letters should be used: http://www.say-it-in-english.com/BasicEnglish8.html

4(Four) days have passed since I arrived at the Philippines.Comment: Using '4' is okay in casual writing, but it is best to spell out the number.

I seems that I to have caught a cold on in the plane, because the air conditioning was too cold.Comment: You may be interested in this -> http://www.bbc.co.uk/worldservice/learningenglish/grammar/learnit/learnitv353.shtml

So today I didn't go for to the lessons and lie on the but laid/stayed in bed.

I went to a big mall in Cebu, called "Ayala Mall", (two)2 days ago.Comment: Names (e.g. Cebu, Japan, Ayala Mall, Kyoto) should be in initial capital letters.

I was surprised that it was extremely big (or huge).

I bought some beers (I love beer!), and water melon and mangoes there.Comment: plural of beer is still beer, unless it is quantified by a number, e.g. I will have two beers, please.

It was only cost less than $10.Comment: You can also use "under" instead of "less than". Another, perhaps more natural way to say this is: I paid under $10 for the lot.

Mangoes are also very much cheaper than in Japan.