Hi A.,
I am coming in late, and haven't read all responses, so please forgive any duplication.
Been there done that, tho wilth only two kids....but similar feelings. Yes, someday you will take vacation without kiddos (and you will miss them!).
you will get the ME time when you TAKE it, it will not come to you. And remember, you are worth it. There is a reason the airlines put the instructions for the oxygen masks as "first put on your own mask before assisting others"--you will be so much more good to your family if you are good to yourself first. it has taken me a few years of therapy to realize this--so you can get this benefit without the angst and $$ !
I think every mom who is honest resents her kids sometimes. That doesn't mean you are a bad mom. And it is OK to feel like crying sometimes too.
You mention not being on anti-depressants--I am not saying you should be (a decision for you and your doc), but I will say that getting out into the fresh air and sunshine does boost my mood a little bit. You might try that, with or without your kids.
Remember to eat right...that sets a good example for the rest of the family too.
Find some way to leave your kids(maybe even just the girls, if you feel more comfortable having just baby with you) with someone for the me time or a date night. someone mentioned what I called a "mother's helper" a kid (can be boy or girl) who is there at your house (or park or beach or....) to help you. Maybe you need to wash the floor and want to do it without little footprints (what a concept!). Have the mother's helper take them outdoors or in basement or living room while you do it. You are there for any emergency (e.g. smoke or blood) but don't have to be disturbed for anything less.
Maybe there is another couple in same situation as you. You and hubby (if home) watch their kids one night so they can go out. Next time they do the same for you.
When I moved to Holland Mich. I joined the Newcomers Club. They had a babysitting co-op. It was a GOD-SEND!!! I am still in touch with a woman I met there (though neither of us live there anymore). Check if there is something like that in your area; or start one!
Good luck, and hugs to you! Hang in there!
K. Z.