My bitch is 5.5 months old. Today I noticed some change on her vulva. It used to be pink. Now it’s brown. The discoloration is caused by some brown discharge. It’s not swollen as some of the images I saw online. The size is the same as before. I’m not sure whether this is her first period. She’s only 5.5 months old. I heard most Sheltie start their first heat after six months or later. Also the discharge is brown, not red or blood color. She’s my first female pet. So I’m not experienced at this. Does this sound like the start of her first heat? If so, how long will the period last? Shall I buy some sanitary pad for her? Thanks a lot.