1) You can get Omega 3s from flax seeds, flax oil, walnuts, hemp milk, hemp oil, and chia seeds. There is no need to take a supplement unless you are being extra-cautious because you are pregnant, elderly or have a medical condition. In that case, algal oil is a completely vegan alternative to fish oil supplements.
2) Vitamin D comes naturally from the sun. Even if you drank cow's milk you were getting vitamin D from a supplement - vitamin D is added to pasteurized milk, and a lot of people don't realize it's not natural. Other ways to get vitamin D without having to take a vitamin pill are eating fortified cereals (like Multigrain Cheerios) or drinking Silk soy milk which is fortified with vitamin D just like cow's milk. People need 20 minutes per day of exposure to daylight WITHOUT sunscreen to process vitamin D...when I lived in Los Angeles I put sunscreen on my face and chest but not on my forearms so I would get vitamin D that way (and on my feet or legs if they were exposed). Lots of people take D supplements in winter even if they aren't vegan. If you eat a lot of white mushrooms you're probably getting some vitamin D. You can also buy "vitamin D lamps" just Google it. They're the kinds of lamps depressed people use when suffering lack of sun.
3) You should know that vitamin B12 is fed to farm animals. Cattle farming is one of the biggest wastes of mined B12 in the world, it's a lie perpetuated among meat eaters that cows are somehow magically able to make B12 better than we are with the state of our agriculture and soil. When you eat meat you are eating the flesh of an animal who was supplemented with B12 already most of the time - so you're still ingesting a supplement. Bad farming practices have lead to this "issue" with B12 that isn't unique to vegans. Many people living in poverty, children and elderly people are B12 deficient even when they're omnis because of junky diets....you can buy Red Star Nutritional Yeast ...it contains B12 and you wouldn't have to take a pill. I like eating it with pasta and marinara sauce, on avocado toast, and in vegan cheez sauces I make at home from scratch. Some people sprinkle it on popcorn or cooked veggies. Vegan milks are often fortified with B12 - Silk is.
4) If you eat fish once or twice a week you are not vegan or even "semi-vegan" because you're not even a vegetarian. Yes, eating fish once or twice per week might be an adequate source of B12 but you would neither be a vegetarian nor a vegan. If you have some sort of paranoia about swallowing vitamin pills, I have tried my best to supply you with alternatives to that. But to imagine you can live in the 21st century without any supplements at all - no matter what your diet is - is a joke. It's an imaginary construct. With farm animals being fed vitamins, antibiotics and hormones, and milk being pasteurized and supplemented, and common cereals being fortified, you're not escaping supplements anywhere you go. It's not like they're drugs I don't understand the aversion, but w/e.
