Get some mirrors, lots of blinkers front and back, and see if you can get one of those neon orange vests. They're extremely visible during the day.
All that should at least make you feel safer if you're totally aware of what's around you.
You can also alter your route and go down wider and less busy streets. It might take a little longer but it'll also be a lot more comfortable. You might even get to work less sweaty and exhausted.