What Causes Vaginal Bleeding While On Levest?

hi, I've been on Levest 150/30 since November/Decemeber of last year and was previously on Microgynon 30. I'm not due to start my period until next week as I am still taking my pill but I have started to bleed. I have missed no pills and this is the first time I have bleed during taking the pill. Is this normal or is there something wrong? I have also had other problems since changing onto Levest 150/30, such as severe mood swings that are affecting my relationship with my partner and family. Please could you give me some advice on what to do about continuing to take Levest? I was told that Microgynon had stopped being produced but I feel that that was the best contraceptive pill for me out of these two pills?