3 follies is good but however the chances of their being a mature egg depends on two things...size, and your e2 levels. For an example of you had 3 follies that were a size 17, 18, and 20 a good e2 would may be around 290-380... or even higher. Now say you had those same size follies and your e2 levels are only 83 then thats not good. And you would be lucky if you have just one...each mature follie should at least have an e2 of 100 to be considered good quality egg. I am not that good with explaining things...so I hope I don't confuse you.
And yes its very normal for them to change doses within one cycle. And you may even create a few more follicles....which is a good and bad thing. Because if you have to many they will cancel your cycle.