Cat wont Stop Meowen all night

Hello: We have this 14 year old perhsion and it is always purring and in good health but for the last 6months all night and now alot during the day it starts with loud meowen (off & on). It is starting to take its toll on our sleep. We cannot figure out why it is doing this? She is not in any pain or anything like that!
   
Does anyone have this problem and what can be done about it,

i don't know why cats do this but it seems to happen as they get older my vet even said this although she could not give a reason as to why it happens but all of my cats have started doing it around the age of 13 but they don't go all day and night so im not sure why that is is your cat spayed?my first thought was maybe the cat was in heat Sometimes cats get fussy when something is going on in the house has there been any changes resently I have also known some to do this when something is medically wrong so being that is a 14 yr old cat it probably would not hurt to have her checked out

Yes, she was spaded, this started happening around the same time our other cat had to be put to sleep, and its gotten worse alot worse since. I was wondering if there is a special collar for cats like they use on dogs to stop them from barking?
   
I dont like using things like that but its getting so bad, we get NO sleep lately?