I did have 3 under 3 until last month, and I would have to slightly disagree with the mom that said going from 1 to 2 was the hardest. My 3rd is probably the best baby ever, however, I have two hands and can fit two kids on my lap, and the third has been the one that has pushed me to my limit.
Some things that helped me with the third was not nursing. It never went well with the other two anyway, and I just couldn't spend hours upon hours making it work, so no guilt, just didn't do it. I keep a strict nap and bedtime schedule. I need time off and need to know that the day will end at a certain time. I have been working with my kids to pick up after themselves so that I am not constantly tripping over toys. I view a successful day as getting one or two loads of laundry done and maybe dishes once, and have hired someone to come in twice a month to do the things like bathrooms, dusting, etc, that I just can't ever get to.
Some things that have been difficult: not being able to do anything without being interrupted. Feeling like I am either a good mom or a good housekeeper, but never both. Getting a shower every day. Getting enough sleep. Feeling like a prisoner in my home. Feeling isolated. Realizing that in a few years the busy will be a little less intense.
Try to take any help offered. Try to get enough sleep, you are going to need it. Try to get exercise and eat right. And whatever you do, don't be too hard on yourself, if anyone thinks that you should be doing something different, they have never had 3 under 3. Try to get some alone time with your husband and keep your marriage strong, you need that to be the best mom to your babies. And be sure to enjoy the babies, they will grow quickly....at least that is what I keep telling myself :)