Are you feeling unmotivated because your heart isn't with this particular lab or because you don't feel you're good enough? If it's the former, maybe with your good performance, you can switch to a lab that is closer to your interests? If it's the latter, I would encourage you to keep going with the counseling and try to ride through it. I don't think it's uncommon to reach a slump late in the first year and the second year. It's a big decision to leave and if you find a way to go through the motions and keep going, I think then you'll have a better idea whether it's a passing slump or a more permanent feeling. If you find it's more permanent after a year or so, then maybe revisit the idea of leaving and maybe by then you'll have a master's through your program. Sorry you're feeling so rough about things.