Could my gerbil be pregnant? please please help as i need to prepare?

ok so here's the story....i've had my two gerbils, bonnie and clyde for about 9 weeks now....they were already 4 months old when i got them so they are about six months old now...the man in the pet shop wasnt sure of their sex but when i brought them home i sexed bonnie to be a girl and clyde as a boy....but they havent had babies together before...they are both the sweetest gerbils, who would fall asleep in my hands for hours on end and just love coming out, but the past two weeks have been different. they had bedding all over their cage and tunnels everywhere, but they pushed it all over to the one corner of the cage and now no tunnels remain, there is just bedding with a hole in the middle, like a nest. And the water bottle is emptying a lot faster. Then when i took bonnie out, she started squeaking and wouldnt let me pick her up, and when i did she started nipping at me to get me to put her down and cylde wont sit still for even a second he just rushes to get back into the cage. this has carried on for two weeks now, and i tried holding bonnie again today, she has a tiny little bulge under her belly but it's very tiny.....and she's still behaving the same way, as is clyde....they just want to go back into their cage to carry on making their nest...please help, is bonnie pregnant???????