Service tax exempt or not

I have a private limited company and my turnover is around Rs. 24 L annually. My 80% of this income is derived from websites like elance and odesk, where I bid for projects. Payment received through PayPal, clients pay in USD, PayPal deposits in my bank after converting into Rupees through CitiBank NEFT. In PayPal it shows both these transactions clearly, what client paid in USD and what they transferred in INR after deducting their fee. I am myself a qualified professional website developer and as a private limited company also we make websites, I have a very less number of employees around 6-8 who are normally paid in the range of Rs. 15,000 to Rs. 18,000 per month. The projects I do, are all of clients from outside India, we make mobile apps and websites for them. They are hosted also in foreign servers, made for foreign clients. In total around 18 L my company earns from the 24 L annual turnover, is due to services I provide to outside India clients and their websites. Indian clients payments never exceed 6-7 Lacs in any year. I have not obtained a Service Tax number also due to this fact. Company is running since last 4 years. I always have a doubt regarding Service Tax and when I search on Google, I think I am exempt from it so I need not take a ST number. So am I required to pay Service Tax or am I exempt under the Export of Services law ?