What do you want more of in your life?
From what you've typed, it sounds like you want less of people (employer, therapist, girlfriend) hassling you over being non-proactive. Thats fine, but it is still a reactive desire.
To be more proactive, you need:
1. Some desire that leads you to initiate actions in the face of uncertainty.
2. The take actions which change things about your life even in the face of fear.
Example:
Suppose the answer is "I want more time spent relaxing". You could then make a proposal to switch to a 4-day workweek. You could then take the risk of talking to your employer about it. There is a risk your employer is unhappy about that.
Take regular amounts of time to reflect on what is working and what isn’t, and be willing to change the things that aren’t working.
When you identify a problem, be willing to take advice and experiment with ways to avoid or solve the problem.
Treat yourself just a little bit like a resource management game, and make sure you invest in your engines of production. This usually looks a lot like eating well, sleeping, exercising and learning regularly.
This may or may not be the type of thing you're into:
https://www.enneagraminstitute.com/type-9
I am this type and it sounds like you might be as well. If it doesn't resonate, then ignore it. If it does resonate, I'm open for any questions :)
Usually this means you don't have a clear goal that you really desire to achieve. Why do you want to perform better at work? Maybe you don't have any incentive to do so. I'd talk about this to your therapist.
Find the environment where you are enough good. And don't listen to that bullies ;-)
Maybe try drugs but please don't shorten your life while chasing for something you might not need, especially if looking at retrospective.
I have the same issue as well. However, after deep reflection I realized that I am not proactive in certain situations and under particular circumstances.
For example: I worked with a boss who was a micromanager. When I was first hired I was enthusiastic and ready to grab the bull by the horns. Yet, a few months into the job I simply sat back and did nothing.
On the other hand, when I find an intrinsic motivation (Daniel Vassallo talks about this), I become automatically proactive.
What I'm trying to say is, do some reflection. Are you not proactive because you're simply not motivated enough due to externa or internal reasons? Or are you not proactive because of other factors? This might give you insight into how to tackle the issue.
On the other hand, ask yourself this question: why should you be proactive? Is it an end in itself, or instrumental? If there's no goal that motivates to become proactive then is it really important to be one?
Hope this helps!