E.,
I have 3 kids too. Mine are just turned 4, 2, and almost 6 months. It is can be very overwhelming! Do you get to have a break ever? I've found that the ECFE program (through the MN school districts) to be a life saver. Of course those programs are all winding down this time of year, but schedules will be out this summer for fall.+++I just saw you are in NE, check your local community education schedules for Early Childhood classes you could take with your kids, they are super fun.
With such a little baby, do you get much sleep? If your 3 year old still takes a nap, make sure you lie down too! Let the dishes sit, take a break so that you can start fresh when they do. I find that when I am tired, my fuse is much shorter. Then I feel guilty for snapping over nothing so I can totally relate to you. Even if the 3 year old doesn't take a nap, make him/her have quiet time or a little TV time so you do get a break.
Another suggestion is to get outside. Now that the weather is getting better, go to the park. The 17 month old is old enough to walk around, play in the sand, sit in the swing, etc. If you can make a schedule for yourself that includes outings in the morning and home by lunch for nap, your day might be easier for the afternoon. Everyone will be tired and ready for a rest, and in a better mood from getting out and doing something fun. Get a baby carrier (a sling or a bjorn) wear your baby at the park or zoo.
This is a hard point, but with summer here, it will make it easier to get past because you can get out so much easier! I really feel that helps us, even if we just go for a walk around the block!
You are a good parent. Best to you and your beautiful children.
Jessica