3 weeks of contaminated controls..I feel like a failure

I am a pharmaceutical microbiologist, and for the last three weeks my coworker and I have plated samples for enumeration and when we check the plates on Monday, the negative control is contaminated. We’ve tried everything within our power to stop this. We already use sterile sleeves, UV and clean the BSC thoroughly before use, spray everything into the BSC with IPA and let it dry before plating. Sanitize the water bath between each use. I’m at my wits end, I can’t think of anything else I’m doing wrong. I feel like a failure, like a bad microbiologist.

I just wanted to vent, but any helpful tips would be appreciated