Crying kitten?

my kitten is a year old. & lately she has been crying. she doesn't whine or make a cry noise, shell curl up n the corner on her bed & shell sit there & tears will just come out of her eyes, its heartbreaking. she was fixed like 5 months ago, shes an inside cat (she scared of the outside) she eats fine & she goes to the bathroom regualrly. she sleeps alot like most cats, she has toys to play with. she stays at my bfs house since we don't live together yet, but i see her every day in the evening when i get off work. so she gets lots of attention & her & my bf cats play together all the time & they sleep together, they are so cute, but im not sure what could be making her cry. shell come 2 me when i call her, she curl up on my big pregnant belly & sleep, but i cant figure out what is wrong 2 make her cry. she doesn't get n trouble alot, only when she gets on the counter, but we shoo her, never hit. what could be wrong?! im scared, what should i do? takeher2vet?