My tomatoes wont turn RED!?!?!?

It has been like 2-3 weeks since i got a tomato bush at this local garden store its pretty cool. and i have 3 humongous tomatoes growing on the tomato bush. fast forward 3 weeks later after i got the bush with the big tomatoes, they haven't changed size or ripened AT ALL! what can i do to make these tomatoes become red and for all the other ones who haven't gotten even a centimeter bigger! HELP!