6 yr old boxer urinating in house

Question
We rescued a female boxer, approx 6 yrs old, about 3 months ago. Izzy had not much interest in food and we had to hand feed her to get her near the food for a few weeks, and she was also being sick quite regularly. I took her to the vets which did a stomach xray and found nothing except that she has a gassy tummy.  The being sick seemed to resolve itself and she has been eating on her own (although she can walk away if I leave the kitchen). Also she urinated on our bed but she was lying down.

This last week she has been sick a few times again.  We go for a walk in the evenings across fields, etc, and Izzy was previously drinking out of the puddles after a run, I couldn't stop her so took to taking some water out with us.  I thought that she could be drinking the fresh water then running and getting excited before the water had settled and that was why she has been sick. But she is sick on nights before she has had a drink too.

Then last night, Izzy was asleep sat next to me on the settee while I was reading a book, I suddenly felt my trousers becoming wet and very warm. Izzy only seemed to put her head up from lying when I started shouting, again it seems like she didn't quite know she was doing it. Izzy is fully house trained and goes out for walks at least 3x a day.

Please can you help by advising us on what you think may be causing this urinating, that is the maain problem.  She has put some weight on since coming to us, but her ribs still show slightly. I'm resigned to the fact that she isn't a big eater and that the weights not going to be put on overnight, but the sickness is very concerning, especially since she had full work up at the vets, including blood & urines and nothing was found.

Thanks a lot.

Answer
The urination is most likely a condition called "spay incontinence" - not uncommon in spayed females.  (You don't mention if Izzy is spayed but since she's a rescue I'm assuming she is.)  Many Boxer owners I know have had success in minimizing or stopping the incontinence by giving a teaspoonful of fresh chopped parsley per day.  

The sickness may simply be something in her diet that's caused an intolerance, especially if a full veterinary workup showed nothing amiss.  If you're feeding kibble, you might try a limited-ingredient formula like Wellness' Simple Solutions:
http://www.wellnesspetfood.com/dog_wellness_simple_food_solutions_index.html

Or you can try home-prepared foods, if you're interested in going that route; a good book on the subject is Monica Segal's "K9 Kitchen: Your Dog's Diet", available at www.dogwise.com or the author's site, www.monicasegal.com

Good luck!