I am like you, decent at swimming and cycling but not great at the running. I used to tell my mom 'the only reason I run for anything is because the bartender yells last call'.

I would recommend setting a time goal of 1/2 hour of running. But don't aim to run solidly for the full 1/2 hour. Run for 5-10 minutes, then walk for 2 minutes, then continue until your 30 minutes is over.

Keep on working on this type of schedule until you're walking less and running more, and maybe this will help you get closer to your goal. FYI I started running only two months ago and couldn't barely do a mile. It was probably closer to 3/4 or less. I would run until I absolutely couldn't any more, then walk for awhile, then start running again. Now I can run almost 3 miles although not at the speed I'd like to be at.

You can do this! (also there are some 'couch potato to 5K in 3 months' plans on runnersworld.com that might help you out!)