The thing with the pill is, as told me by my gp and practice nurse when i went on the pill both times, is that it works by fooling your body into thinking you are pregnant.
And when you are pregnant, your body is programmed to make you eat more so that your baby is nourished.
So, as a result the pill can encourage an enlarged appetite, but without the baby to feed, so a gradual increase in weight is likely.
The two options are to be aware of this, and conciously keep an eye on it so you dont eat more than you need to for one, or do more exercise to burn the excess off. Or do a bit of each!
The other thing that the pill can do, is change your body shape. Your hips are more like to fill out, and your breasts enlarge- both things that can happen during pregnancy due to hormones. So even if you dont gain weight your shape can change to make you feel larger.
You may also experience some water retention from being on the pill, which can make you feel bulkier.
You could discuss your problem with your GP, as there are various pills which have slightly different side effects, and he/she may be able to find one which has less weight side effects.
Otherwise, just keep that eye on portion sizes and snacks. Nuts are good for you, but can be fattening if you eat too many.
I would also alter your exercise routine to include some muscle building and toning, not just cardio, as muscle will burn more energy, and toning will improve your shape.