Debbie, no expert on this (26 weeks pregnant, first baby) , but from what i've heard from other mums etc, may be an idea to go to a physio to check out your pelvic alignment (pregnancy can knock it out a bit or something), may give you exercises and advice on how to build up your muscles and running without injury, there is an excellent thread Pregnant Runners club and lots of them have great advice on running pregnany and running after pregnancy.