Pregnant or something else?

[canadiandawn]

Hi all. I have a 20g freshwater tank with some mollies and guppies. One of the mollies has had fry twice now, the last time being 6 weeks ago. We thought she was about to have more but are now thinking maybe something is wrong. I've never seen a molly this big before:



She isn't even swimming right.....it's almost like she waddling.

Anyway, does anybody know by looking if she's about to give birth or sick? I should note that all our other fish are healthy so we're pretty sure it's not sickness.