Really? Its difficulty is too high, right? Can you tell me how many coins you have mined until now and how long when you started to mine?
diff 600 is probably half to 0.9 coins a day in this one so that's something else maybe pool was unable to find a block. People should joind the pool that has decent hashrate or the get nothing. Especially with Nicehash if you dig at the pool and Nicehash digs elsewhere. At least you piggyback at Nicehash and get some low diff blocks percentage as reward if you're at the pool where Nicehash is at