I'm 6 months into my PhD

I've completely run out of motivation - really simple experiments keep going wrong and I'm finding it increasingly hard to care. Everything's starting to feel like I'm just walking on a treadmill all day and not going anywhere, I'm starting to worry that I'm just not cut out for it, having spent the last 6 years in science and the last 3 trying to get a phd.
Is this just a 6 month itch? Did you guys have it and get through it or have I got a real problem here?

This is more common than you think. Take a short break, see if that helps, perhaps talk things through with someone but a PhD is rarely straightforward. Don't think you're alone because you're not.

This sounds far too familiar. I'm in my third year now and, looking back at my PhD, I think I had phases of feeling ok and having fun, and phases where nothing was going right and I couldn't help wondering if it would be a better plan to quit and get a normal job.

I don't really know what to suggest, but I'm fairly sure that it's a perfectly normal thing to be going through.