I can't speak for Yasmin personally, but I've been on Dianette for my acne for about two years now. Birth control generally stabilises oestrogen levels (it works by releasing synthetic oestrogen, which regulates your natural oestrogen and stops it from peaking mid-cycle, which is what causes other hormones to be released that develop/release the egg).
With any medication really your body needs time to get used to it. Every pill you take contains hormones and it can have side effects cos your body isn't used to little hormone spikes you're introducing every day. The pill can cause headaches and mood swings as well as nausea, appetite problems, breast tenderness etc. For acne it usually takes at least 6 months to see any real improvement, so your body does need a little while to get used to it!
I never personally had significant mood swings, but I read about a girl on Dianette who cried for 20 minutes because her sister sat on her chocolate bar
Best to let your doc know, he can bring you in and offer you some advice on what to do. I see you've made an appointment, so see what he says - he might just tell you to try it for another couple months and see how you go. Some people just can't tolerate it, so it might be that you have to try something else.
Edit: I also wouldn't take a break from it. If you're on it for acne it can come back with a vengeance (sometimes worse than it ever was before) so if you've not been on it for long I wouldn't recommend coming off, unless it's causing you significant problems.