I started the mini pill before that with all of mine and b/fed older two up to 11 mths and am still going with dd3 (17mths). I don't think it is supposed to have any impact on milk supply and certainly my experience bears that out. You do have to take it and roughly the same time everyday though and you may have some intermittent bleeding or spotting for a few weeks whilst it settles down. Also - when I've taken it and then wanted to get pg I found that my fertility returned very quickly so bear in my mind that you can't muck around with it - if you miss a pill or are later than three hours then you MUST use alternatove contraception for two weeks - unless you want to experience tandem feeding
Combined pill is not used whilst breastfeeding but mini pill is fine - with the drawbacks I've pointed out already. Having got to 11 weeks your supply should be really well established - and look on the bright side - you've probably got more time to errrrrrm NOT abstain than you had a few weeks ago! You have to take it for two weeks before it's effective as well so you can break out the condoms or carry on abstaining for a fortnight yet!
I'm on cerazette which is a mini-pill, but with the advantage of being able to take it within a 12 hour window, not the usual 3 hours. I have heard some people say it makes them feel a bit crazy, but I can't say I've noticed that... anymore than normal, anyway