I'm not a lesbian so I can't relate there, but I AM a mother and believe me, all women go thru that just before the baby comes...usually the last couple of months are the worst. We feel ugly, fat....ugly...and add to that your natural feelings of not being particularly 'femme' I can well understand how this must be incredibly stressful for you.
Just try to accept its the hormones talking, preparing you for the jetisoning of your baby from you....I think it's safe to promise you will feel much better after the birth.
Both you and your fiance are in my thoughts