Baby always exhausted?

My baby is 6 months old and is always exhsuted, and just screams when tired, its impossible to take her out places as she just goes hyterical when she is tired. I am also trying to wean her but she just screams, I try to feed her as soon as she wakes and after naps but even then she is tired. Are 6 month old babies always this tired? I see other babies at baby cles and they dont seem like this. Any advice how I can build up her energy. She is very very very active, never stops kicking playing etc! never has a calm second, she has a good bedtime routine goes to bed at 6.30-7pm following a bath and some light music. any help would be great, any foods that may give her more energy, just giving veg and fruit purees at present with some cereals