ok thanks guys for your replies, next time I will check the number of unconfirmed tr. before giving an order for buying
What you should be checking is
the transaction fees that you need to pay.
The exchange I am using (coins.co.th) does not allow me to chose a transaction fee when buying btc
As soon as possible then, you should be moving your coins to a wallet which you control. Otherwise any problem with their fee estimation system is a problem for you. If you don't own the private keys, you don't own the coins.
As a noob, am wondering how can the btc future be influenced by this and what are the solutions to it?
-Various solutions to try and increase efficiency (e.g. using SegWit)
-Offchain/second layer solutions like the Lightning Network
-Block size increases.