Looks like Ella has ovarian cysts. When we adopted her on May, I noticed that her nipples were a bit bigger than it supposed to be for her age, and it's a bit crusty. RSPCA said that she has been recently seen by their vet and no issues were found, so I just took it as her normal, but I always monitor it nevertheless.
Anyway, the other night, I noticed that her left side belly seem to be losing hair. So I checked her and her right side also have some hair loss but not as much as the left. I know this can be a sign of ovarian cysts. After I noticed that, I realised that her and Vegas constant chasing and trying to hump, etc. for the past few days probably isn't just a sign of them getting on with their closer bond now. Vegas has also lost some weight because of this constant chasing between them 2.
Hubby booked an appointment for Ella this afternoon at our local vets and she might be having a spay soon. Hopefully ovarian cysts is just the problem. Apart from those I said, she is healthy and still acts as normal piggy.