J., It is NOT your sole responsibility. The children are your children (collectively) as a couple, therefore the burden/responsibility of these kiddos - and all things involved - fall on you both as parents.
I think it is very important you find a time/place, quiet and without interruption, for a talk. Be very honest with your spouse about your resentment and the imbalance. I would hazard a guess there are otherthings you assume full responsibility for (carpool, soccer, etc.?). Practice your speech, making sure there is no whining, no anger, just deliver it matter of fact. Keep the emotion out of it - it is so easy to sound like you're complaining... don't. Have a very straightforward conversation, as if you were discussing an investment. What you feel is justified, and legitimate. Part of a strong relationship is honesty. Holding back is a form of dishonesty. Taking more than your fair share of someone is also dishonest. It causes an imbalance, that if not addressed, can easily grow.
When you've talked to him, did you talk about this problem done in a heated or emotional fashion? Was it done amidst the interruptions of life, dinner, family time, etc.?
It's important that while you may not be the bread winner of the household, your salary/career is recognized as important. I assume your home requires the additional income. As a supportive spouse, your mister needs to respect your career, and the demands thereof. Does he also realize that what your daughter sees in your relationship is what she will most likely mirror in her own, when she's an adult? She could be the one taking more than her fair share, but chances are, she would end up being the one bearing the load - like you. Is that what he wants for his girl?
You need to have a heart to heart with him in an environment that will not allow interruptions. He needs to understand the importance of your job for you, and your family (financially), and the demands the job places on you - thus emphasizing WHY your PTO is so important. This is NOT a financial issue. PTO is totally unrelated to finances, our employers give us PTO so we can have time to de-stress/attend to personal issues in an effort to perform better at our jobs.
Ask him how he would feel if his PTO time were never there for him to <insert whatever he does w/his PTO>.
If he refuses to listen or share the burden, you need to enlist the help of someone he respects. His parents, a pastor, a counselor. I promise you, if you don't stand strong, you will forfeit in other parts in your life/relationship... other things that are important for YOU.
The resentment will fester, and any imbalance anywhere in your relationship will become apparent, and your discontent will grow. It's how we work as humans.
Marriage is a partnership based on sharing and support. Sometimes partners take advantage of one another - and with no mal intent. THey just sort of act like stingy little toddlers and I believe, the majority of the time, they don't see it, or believe that's what they're doing. It sometimes takes a third/outside party to parent away those bad habits in the adults we love.
I hope this helps. I've dealt with this in my own son (he's 24) and while he has no kids, he wasn't pulling his weight around the house while my DIL worked long days too... :O) I also know from experience this emotion, as I dealt with it in my first marriage. YOu have to not let YOU get lost while you're wearing so many hats - we're good at that, as women.
I know I'm getting long winded - but what else do you do with your PTO? Does it always go to kid related things? I mean, what do you do for YOU, J.? You're a photographer... Do you ever use your PTO to attend workshops? DO you cancel weddings because the kids are sick, or does he step in? What would happen were you to be faced with that dilemma?
There are some amazing photo workshops coming up in Seattle (weekend/evenings) over the next couple of months - I can email you the links - they range from 20-60.00 - if you're interested.
Does your family ever use your & Hubby's PTO for family things?
What happens when you're not available for the kiddo things? Does your girl just not go to the doctor? Does she miss her dental appts?