i hope you listen to what Aunt Mel Mel has to say - it is VERY dependant on the child, how much of a challenge it is to get them to hear and obey. take with a grain of salt anyone who says, "oh yes, every time!" yes, they may have an iron fist and their child is super super obedient - or it could be that their child is an "easier" kid. like i was a kid, i was SO sensitive to reproach and discipline, i very rarely had to be asked ANYthing twice, because i was that kind of kid.
now my son, on the other hand....lol. he has his DAD's personality. luckily for us there is just the three of us, and we can afford to be a little more easy going. there aren't two or three or four kids wanting/needing mom's attention, so there is more time and patience to go around with one kid. so yes, my son is one that has to be told several times. he also has a focus problem so even when he DOES intend to do it, he often has to be "reminded" several times if it is a task that takes more than a few seconds. on the other hand - we must be doing something right because we get nothing but compliments when he is with other people. he IS eager to please and really wants to do what he's supposed to. so it depends a LOT on the child.
it's possible, that the words, "okay mommy!" with that giant dimpled smile, is one of my favorite things about being a mommy :) it is priceless. and i probably get it about 1/2 the time. then some of the time it's having to ask a couple more times than i'd like...and occasionally, the battles you are going through. but we usually nip them in the bud pretty quickly because if it's obvious he doesn't WANT to do as he's told, he goes straight to time out.
sorry this is so long - but some more things to consider, are growth spurts, activity level (since it's getting colder are they getting enough excercise daily?), diet, too much sugar, etc. it ALLLLL factors in.
and to answer your question (finally) NO you are NOT alone!! and it does NOT make you a bad mom. hang in there!