Yes, it's tiring and stressful, and no, YADNBU!
You also sound like you're doing a pretty fab job! The beach!!!! By yourself! With two of them!!!!

I have a 3.5 and just gone 2 DCs (17 months gap) and as someone above has said, it is RELENTLESS!
but also 
What kills me the most is that pre-kids, I used to go to bed for a restful night's sleep. Now, the night is just another part of the working day.
Even now, the night is still hard work, sometimes get through until 5.30am without being wokrm up but rarely. I keep DC2s door shut as he wakes me up just crying out as he turns over and goes back to sleep! 
And yes, my DH hates the "minute I step in the door, you're in my face" but I just can't help it sometimes, he comes in to chaos as I cook tea around two tired toddlers and I just vent when I see him (or ask him for a hand, which is even worse
)!
BUT....it has got better since DC2 was a baby. Bit more independence from them both, DC2 at least will play quietly by himself
, bit more sleep really, and more dialogue and enjoyment of things - arts, activities, freinds, etc
So, chin up, keep on keeping on. Your ace and you can only get acer
