Hi kirsty,
I actually ended up with a really bad chest/throat respiratory tract infection when i was about nineteen weeks as well it's really not fun! Keeping the fluids up is great, maybe get down to your doctor, to make sure it is just the flu and not an infection - if you don't catch it early you'll find it'll stick around for ages and obviously we can't get as strong-a antibiotics either, so one course doesn't do the job (in my case anyway). Try and take it easy *bug hugs*, hope you're feeling better soon!