Whole host of stuff to unpick here.
I'd agree these private companies are probably after your shiny pennies rather than being overly concerned about your wellbeing, but I think this is conflating the issue.
Low test can cause a wealth of problems in men. I half use for gym/muscle purposes, half use for mental health purposes. I was low test (like yourself, just above the baseline for getting it on the NHS, but still low) and had anxiety, panic attacks, could hardly eat properly, and like yourself I was put on drugs that are fu**ing poison. I'm not one of these "big pharma is evil man!" types - I bow at the feet of the likes of Pfizer and Astra Zeneca for getting us out of the s**t show we've had for the past year, but anti-depressants/anti-anxiety drugs are over-used, over-relied on, and often make things worse. It's like having a broken arm and just dosing up with morphine - sure the arm stops hurting, but you're not fixing it.
If you're low test, injecting test fixes it, and then some. I'm a different fu**ing person on test and the past year without it has confirmed that. Fortunately sitting in the house doing f**k all has been the law, so at least lack of it made me comply...
So - well done for coming off the Prozac. Nasty s**t that shouldn't be relied on long term. Well done for looking into your test levels. They do fluctuate so yeah, the average of your figures could be the cause, but I'd bin off these private companies. Go to your GP, explain your issue, tell them you're thinking of using test anyway or that you are doing. They'll give you a base reading (did the company take proper venous blood tests btw?) then you can go from there.
Few more questions -
Do you have a mortgage with a life insurance policy, a private healthcare plan, etc? Some people warn against telling your GP you're self-prescribing test (or "using steroids") for that reason as it allegedly can void such policies, even though I'm yet to see evidence of this.
What are your goals here? Is it just mental health or are you looking to improve physique too?