As a personal experiment, I recently spent two months as a vegetarian/vegan, just 'cuz.
I ended up losing 12 pounds without intending to, but my strength continued to improve. It was "interesting" overall, but it's not something I could do longterm, if only for financial reasons (I found it to be hella-expensive).
What do you mean by "vegetarian diet"? Lacto-ovo (allowing eggs and dairy), lacto (allowing dairy, no eggs), or vegan (no animal products)?
Do you still do soccer? If so, you have no reason to secondguess a higher-carb approach.
If you're able to eat dairy, then a protein like Metabolic Drive (micellar casein/whey mix) would be a solid bet. If dairy's a no-go, pea, hemp, or rice would be my next choices.
But there's absolutely no reason to be living on shakes. I'd limit them to one, maybe two, on non-training days, in addition to your usual workout shake on lifting days.
Grains, beans, lentils, nuts, seeds, fruits, vegetables will give you plenty of options for relatively-high protein, high-calorie foods. It'll be drastically easier if you're going lacto or lacto-ovo.
To quote the scary-ass shark in Finding Nemo, "Fish are friends, not food." So no, if you're any kind of vegetarian, fish oil isn't an option.
When I first dropped Flameout from my diet, my skin did get noticeably drier and my knees got moody, but I made an effort to bump up my olive oil, had a handful of walnuts, almonds, or pumpkin or sunflower seeds everyday, and I had avocados on a regular basis. I also threw some flax on the occasional salad when I remembered.