I'm assuming that you are using uk terms and not american.
You are wanting to do a 3 stitch cluster right?
I you would yarn over, insert the hook into the required stitch yarn over pull through the stitch, yarn over again and pull through two loops on your hook, (you'll have one loop plus the loop from the previous stitch left of your first stitch in your cluster) now yarn over again like you're doing a new stitch and insert it where it tells you to, yarn over pull through the stitch, yarn over again and pull through two loops on your hook, (you'll now have 2 loops + the previous stitches loop on your hook left),repeat these last steps for the last stitch and now you have 3 loops + the previous loop from the stitch on your hook, yarn over and pull through all loops and poof, ya got yer cluster. Just follow these steps for any amount of stitches you need in any particular cluster, whether it's two or 5 or more.
Basically, what you are doing is making each stitch to just before the last yarn over and then on the last stitch in the cluster you yarn over and pull through all the loops on the hook.
There fixed it. Sorry, had to do a hands on (it's been a while since I've crocheted LOL)