New mouthpiece

So, I got my new clarinet mouthpiece on Saturday in the post (yes, I bought it through ebay. Yes, I know there are dodgy people on there, but this seller was all sweet and kept emailing me, even after I said I'd received the mouthpiece and gave me advice and stuff... which was nice. :) I also know that ebay can be unreliable, but so far my buys have always been reliably delivered, although this was the first relatively expensive thing (when I say that, nothing has come to over a fiver in the past). Also, I know one is supposed to try out different mouthpieces before buying them, and I did, including the model I bought, which was a Vandoren 5RV lyre (I don't know where to find a lyre symbol, but it is a symbol, not the word)) and the first time I play it it sounds as if there's air leaking out and the tone colour isn't all that great. Which was rahter a dampener on my spirits. So then I play my clarinet lots over the weekend and try out different reeds (and more reeds on Monday night too as I bought a new box of them) and finally find some good tones and colours and sounds, which made me happy, and I continued playing for the joy of playing as opposed to trying to save my clarinet playing as previously. And then there was orchestra today, and when playing my solo bit in 'December' (yes, I know it's March, but we're taking part in the Music for Youth festival tomorrow and for some reason we're playing that piece and I have a solo in the middle section) I kept squeaking. And squeaking just isn't a good sign. I'm going to have to play lots this evening to try and discover the reason for said squeaking and to remove the problem. *hopes to be able to* Hmph.