Female Budgie Acting...weird

i have a female budgie who until recently was pretty normal. she started molting and her and my male bred. i dont think it was successful since she never laid an egg but now she is laying completely flat on her belly for most of the day. she has a very faint yellow staining above her cere. tail bobbing and seems to be having difficulty flying. I seperated her from the male in fear of her being sick and spreading it to him. im worried about her but she seems to eat and drink like normal. i know they miss each other as i put the cages close enough they can chirp at each other and not be too lonely. the male has now started humping EVERYTHING in the cage. could the female just be egg bound? if so what should i do? im use to Big parrots not small budgies but i love my birds and want to help them. am i over reacting and shes just ready for round two of the male or am i justified in thinking she may be sick? please help