I've been veggie 30+ years, I've been very slim and overweight and all in between.
Vegetarianism isn't the cause of an unhealthy diet, that's down to your choices. Just as an omnivore diet can be healthy or unhealthy.
Pizza and chips is veggie but high cal and not particularly healthy, whereas a veggie stir fry with healthy home made sauce and rice is healthy and can be low cal if you don't overdo the rice.
Burger and chips is omnivore but not really healthy whereas a lean meat casserole can be healthy.
Some of us are fine with quorn and soya, but not certain meats. It's now known that especially highly processed red meats are not good for the gut.
Iron deficiency isn't a definite with vegetarianism either. I actually had a couple of bouts of anaemia when still a meat eater, but have never had any problems as a veggie on that score.
We'd need to know much more about what you eat on a daily basis to be able to advise.
With any diet you need to eat foods from all food groups, including carbs, to get all nutrients and eat a wide variety of foods too.
I've known meat eaters with ridiculously unhealthy, very limited diets (like they only eat 6-8 items!) and were often unwell. Their diets were far more restrictive than any of the veggies or vegans I've ever met.
Though I've also known very unhealthy overweight veggies who lived eating far too much pasta, cheese, chips, bread, creamy sauces, high fat dairy, sugar/sweets, crisps etc.
A crap junk filled diet is a crap junk filled diet regardless of whether veggie or omnivore.