Just because I love solving problems:
1. Test your headlight globes (with a multimeter on continuity) to make sure that the low beam filaments are still OK - If you have a short circuit problem, it could be destroying these filaments as soon as you replace the globes.
2. Same goes for your low beam headlight fuses, test them again.
3. Test terminal 86 of the low beam relay to confirm that you are getting power at the relay when you switch the lights on. You need to remove the relay and test the connector that 86 plugs into. The bottom of the relay has the terminal numbers identified. There are three terminals on the relay that point in the same direction, terminal 86 is the middle one at the outside. You need to test where terminal 86 plugs in to see if it's getting 12volts. If not, there is a problem between your switch and the relay.
4. Remove the connector from the rear of your headlights and confirm that you are getting power at the low beam connector.
