That's probably the problem. It's only been the last couple of days though. I normally make at least 2 deposits per day and they have always confirmed in less than an hour. I've added a minimal fee now and will see if that speeds things up.
You should always add a minimal fee ... blockchain is gettting "slower" these days
https://bitcoinwisdom.com/bitcoin/difficulty and most of the pools are being reconfigured to not accept zero-fee transactions (due to BTC/USD price pressure) ... so you really should always add a minimal fee (bitcoin-core client 0.10 makes this easy since it has dynamic fee calculation).