You say "But basically i feel like I don't track things correctly all the time, or at least as smoothly as it was before the incidents. Or that sometimes it takes my brain longer to process everything, leading me to feel more overwhelmed. "

Those are both symptoms of concussion and side-effects of mirtazapine.

The slowed thinking is very common and should not be a cause of concern. it will take time. As you noted, anxiety can make it worse. There are two types of anxiety common to PCS. Thought based, "I'm going nuts. Is this ever going to get better? Oh xxxx, I bumped my head again." etc. Then there is the physical/mental anxiety of a brain that simply has been overstimulated.

Before seeking drug treatment for anxiety, you might consider how stimulus can be reduced.

For many of us, getting a NeuroPsych Assessment done has allowed us to understand and accept these symptoms as real. Even an ImPACT test can sometimes help show your slowed thinking. Sports Concussion Clinics can often administer them. But, without a baseline, the results will be harder to interpret.

Even though your alcohol tolerance appears to have returned, you should still limit your alcohol intake to a single serving while your brain continues to heal.

What else are you doing to help your brain recover ?