Let me assure you that these are completely normal feelings. Babies and toddlers are pretty needy creatures...I believe you commented one time on their care being "constant". As Molly becomes able to satisfy some of her own curiosities (by playing, crawling, etc.), the "constant" thing becomes making sure she doesn't injure herself, get into something she shouldn't, etc.
One thing I've shared with Denise is that a nurse, during Childbirth classes, said that it is O.K. to be frustrated when your child will not cease crying (after you've tried EVERYTHING!). She suggested placing the child in a safe position (baby bed, etc.) and walking outside for five minutes, and then returning. I thought, "What kind of parent could do that?", and then one day after Brad had cried for one hour straight, I very calmly put him in his baby bed, and I walked out on the front porch for a few minutes. Those few minutes allowed me to clear my head, and return calmly to my crying child.
In a nutshell, you're experiencing what every parent experiences. I know you and Denise already do, but continue to help each other have small breaks....it helps keep your sanity during this trying time.
Hang in there.....we love you!