Baby constipation

I think my little girl is constipated. She’s been trying to poo nearly 2 days she keeps pushing and pushing and pushing and nothing is coming out. She’s had pouches of prune yet still nothing what else can I do to help her? We have done bicycle legs and massage her belly yet still nothing is working She’s nearly 8 and 1/2 months old and usually the prunes help but they haven’t this time