Been there 4.5 years ago with our German Shepherd 11 years old and it was a really rubbish 6 months, vets could not find what the problem was, in the end cancer of the colon.

Basically she had the shits for 6 months, then one night lay on the patio and could not get up, phoned vets and they said bring her down ( 9 o'clock at night ) because it would be cheaper than coming out, after spending £1500 over the 6 months i said i don't care how much it costs she going to put to sleep at home.

4.5 years later it still chokes me as i right this.