My healthy yellow lab that is 4 and a half isn't acting herself?

she is beautiful and is usually so energetic and loving... but lately( for about a month now) she has been peeing her bed and acting weird... she will be happy around walk time, but she seems depressed... she looks guilty a lot and pees her bed a lot... and my dad doest want to take her to the vet because it is"a waste of money" but even he admits she is acting strange... she is also very tender on her legs... she wont even jump out of the back of the car... yet she used to do it while i was opening the door! i don't know what to do. it is like she aged really suddenly and badly!