I'm not currently pregnant, please forgive me lurking around in here - I'm having nostalgia as I was starting my labour with my DD this time last year!
Anyway, I put on 3.5 stone, much of it in the last trimester (though I know I put on about 9lb in 1st tri as the only way I could stop myself spewing was to eat all the time!). I lost a lot of it straight away - over 2.5 stone in the first 3 weeks pp.
I struggled with the last stone or so, but started slimming world at 5.5 months pp. I'm now 12 months pp and I am 17lb below my prepregnancy weight. It's taken work, don't get me wrong, it didn't just happen, but as long as you have no underlying medical conditions (thyroid, pcos, etc), if you put the work in, you will lose it. I still have a squishy tummy, but it's gradually tightening up. It will never be the same, but that's ok.
I will say, though, in the early days/weeks, seriously, just don't even think about it. Enjoy that baby, look after yourself, and take it as easy as you can. Eat healthily, but don't eat to lose weight. Your body needs to repair and replenish itself after everything it's done over the last 9 months, don't punish yourself for not 'snapping back' to how you looked prepregnancy!