The bump is making me leak!

What # baby, Canadianmama? How many weeks do YOU think you are?
A bit of a UTI / minor bladder irritation seems like the most reasonable explanation as your body is adapting to this pregnancy and different filtration rates, progesterone relaxing the urinary tract, etc. However, somewhere in my head are the rambling thoughts...detrusor muscle....overactive....interferes with the urethra and surrounding muscles and ability to hold in urine. Not sure though, and even if I am right I have no idea what you would do about it. Off to have a look see...

Usually by baby #4 the uterus is springing up out of the pelvis so quickly and so high everyone starts jabbering on about twins! Certainly doesn't sound like 12 weeks at that height...
Could still be a UTI if the irritation is in response to sugars consumed during the day, perhaps?

Congratulations, if I have not said so already!
about your doctor and the dates being different- great news is that you are on the later side so no pressure if you go over 40 weeks- The only potential problem is that if you go early (like 37 weeks) the Dr. will be concerned since according to them you will be 35 weeks. I have found the best way to get what you want (if you are absolutely certain of your dates) is to have your husband come to your next apt and insist that your date is correct b/c he was out of town during their supposed conception date.
However- if you wait it out a bit longer they will realize they were wrong- and adjust your dates accordingly.
on to the urge incontinence if you even want to call it that- the other type you describe (the jumping kind) is related to the muscle strength and it sounds like you don't need to worry about that. Though I would continue to do a few pelvic floor exercises each day to remain in communication with that part of your body. Sounds to me like a nerve issue- later in the day you get more swelling right?- like when you wake up in the morning your tummy looks much smaller than at the end of the day- so maybe some of the swelling is causing some kind of block and you are not getting the message to go pee soon enough.
here is what you might try...through-out the day get on your hands and knees (maybe once in the morning, once before lunch, and twice before dinner) and rock your pelvis about 100X- arch up into a cat stretch and bring it back to neutral- end by going into child's pose- and then slowly get up and go to the bathroom and go pee. By assuming this position you will encourage your bladder to get into it's proper place and take the weight of the uterus off the bladder and maybe you will be able to sense better when you need to pee.
Hey. try this tomorrow and report back- if it doesn't work we'll think of something else you can try....
one more thing that helped me was to get up and drink a very big glass of water- it got me in the habit of drinking in the earlier part of the day so that as the pregnancy progressed I didn't have to get up frequently at night to pee.

I had an asymptomatic UTI during my 3rd pregnancy- that went undiagnosed until I peed blood- but what I felt was exhausted all the time and I had some serious lower back pain- so watch out for those things
also my experience with fundal height is that depending on the mom the uterus is pretty sketchy for predicting dates until it hits the belly button- and then you can guess about 20 weeks or so....With our 4th the top of my fundus was in between my belly button and my mons pubis at about 14 weeks-

I had the opposite thing happen with my 4th. Ultrasound showed my uterus to be tilted way back (I only had it done because I thought I was miscarrying), which was the reason given that we couldn't hear heart tones.

Re: UTI, it never hurts to add some cranberry juice or pineapple juice to your diet just in case. Pineapple actually contains more D-Mannose than cranberry. Before I learned how to pee properly with prolapse, I had a chronic UTI. My pee stank! I started drinking canned pineapple juice (I prefer raw for obvious reasons, but that many whole pineapples don't fit into the budget comfortably), and the juice from cans worked very well.