It tajes about 2-3 days for the sperm to regenerate and be thick again. If you are sexually very active, either by sex act or by playing with yourself, spanking the monkey, your sperm thins out and becoming more runny. remember, 90% of the white stuff is actually alkaline fluid (so that the sperm survives super acidic and harsh environment of a vagina) and only 10% the actual sperm. It is like running- you must rest between runs, if you don't your performance will suffer- let your muscles fillup with glicogen again and let your body clean up lactic acid. So with the sperm- give it the time, it is very precious comodity of your body.