I am on a 40 dollars a day budget can I travel around thailand for abut three months

no problem , find some cheap motel to stay $10-$20 a night, eat at local stall-$1 and buy beer from supermarket or 7-11 . take the bus and some fun in the local ktv pub.

If you can stay in cheap guesthouse On khaosan road have small guesthouse which is 5 usd (1 us-33 baht). so that's make you have 1000 baht left for everything eles. I bet you won't do thingssss everyday there must be a cheap day and expensive day.

You can eat 3 meals will cost you 200 if you not fansy the big restaurent.
Come as a backpack live cheap and not much of Girls paid you will be just fine.

Same as on island you should visit some..in krabi :)

you could do it. 40 dollars is a little over 1000 bot and that's a lot of money in thailand. (i just came home from thailand) you couldn't stay at the nicest hotel every night, or eat at the nicest restaurants every night but that's not to say you couldn't some days. go for it! just make sure you have enough money set aside for a plane ticket home.