That’s really low levels at 18, you should be north of 1000 ng/dL (34.7 nmol). SHBG is low enough that anything less than twice weekly injections will just drive down your SHBG to a level where it won’t be as effective. SHBG are the cards at the poker game, you can’t play the game without the deck of cards, it hands out the free testosterone and estrogens to the body to affect you in a meaningful way. Large doses will lower it which is why you require smaller more frequent injections, your problem is the doctors in your country believing injections every 2-3 weeks is idea.
My SHBG was a few points higher than yours before I started TRT, it rests just below 20. When I was originally put on TRT my doctors gave me 200mg injections and I felt terrible, worse than pre-TRT. I figure at some point doctors are going to pull their heads out of their butts and realise these 2-3 week injection intervals are wrong. It doesn’t matter how much testosterone you have, if your SHBG is too high or too low it won’t matter, you’ll feel as if you have no free testosterone. You don’t have the proper tests in your country to run a sensitive estrogen test which would help determine if your gyno is estrogen related.