Today i am stating to notice a clunking noise coming from under the bike somewhere, maybe the chain. When i am 2 up it seems to be the worse. Only happens in first gear when i am starting up at arounf 15mph or so.

Faster then that its fine , or at least i cannot hear anything when the engine is louder.

Could it be my chain is loose?

check the slack of the drivechain

my guess would be that your right, you're getting chain slap because the chain is too loose. when the second person is on you shouldn't hear it as much though because the chain should always be somewhat tight unless there is alot of movement on behalf of the passenger. if the passenger is moving around or you hitting alot of bumps it would make sense that the slap (funny noise) would be worse because there's that much more tension on it all at once.

With a passenger, the suspension might dip down enough that the chain slack hits against something. Like the swingarm or frame.