My lil girl rhylee is 4 1/2mths.. she is bottl...

My lil girl rhylee is 4 1/2mths.. she is bottle feed with Nan formula but after the rest of the family getting a gastro bug (never got rhylee), she started with runny poo's with alot of mucous and vomiting more than the little amount but lil less than projectile about a month after we finished being sick. she wouldn't feed properly, fought the bottle and screamed at the site of one, become very irriatable and generally just not happy (b4 this all started she was happy drinking 4 x 250ml bottle and very happy).. this continued for about about 2 weeks so we went to the docs with me in tears cause runny poo's still hadn't cleared she was still vomiting both still with mucous and very irriatable.. explained it all to my doc and he said that sometimes when lil ones get even a lil hint of a tummy bug it can make the temporaily lactose intolerant. so we switched her to a lactose free formula and had her poo's tested. she is going great on the lactose free formula, all vomits are only a lil from her being to piggy, and shes back to her happy self... (she has been on this formula for about a week ) only thing now is her poo's where great and we where getting "normal" ones but now she seems to be having trouble passing them..I wouldn't call it constipation just yet but maybe a lil smear in her nappy and thats about it... test results came back as normal for the lactose test... My dilemma is apart from pooing she is going great on this LF formula but lil concerned about the poo...tried her on the nan formula today and she has been chucking ever since she had it.. If the test came back normal would i still beable to keep her on the lactose free formula and if i did is there anything i can do to help her poo better?? would it do her harm keeping her on the formula if she is NOT lactose intolerant?? would adding an extra 10-20mls of water into her bottle help?? any ideas would be appreciated..and I hope that all made sense.. Thanks Emma and Rhylee