Why was my female dog humping my legs?

she is a 3 year old cairn terrier female names brandie. she hasnt been getting much attencion recently. maby that has something to do with it. we have 4 small dogs and shshe fights with our other female cairn sometimes too. she is fixed too and could never have pups cuz she had a hernia and had to be fixed right away. she used to do this when she was a pup too. mollie,the cairn that she will sometimes fight with had a litter of pups (now shes fixed too). im only 14 and started humping my legs which were out crossed in front of me crossed!!! sicko! alsio she licked another of my dogs butt after sniffing it. shes acting real gross and weird. (we just had to do our yearly shaving so she dosnt even looklike herself lol) what is wrong with her?