First of all I completely understand why you feel lonely. As you say, you do not know any other vegans and therefore you probably feel very isolated right now. This is made worse due to the fact that you are also receiving negative feedback about your vegan journey, but Laure, let me be the first to assure you that there is no need to feel isolated and alone.
This forum in particular has hundreds of members, many of whom have been through exactly what your going through. You will find that we are a very open bunch and should you ever need advice, need to vent or just a simple chat when your feeling down there will be people here for you.
Being Vegan, or Vegetarian will always form some kind of "us and them" segregation. People are set in their ways, and the truth is many people consider that their morals have been called in to question when someone close to them adopts a cruelty free diet. People may become paranoid. They may think that by making the personal decision to turn away from animal products you have in some way took a judgement against their own habits.
People are very defensive, and I have found that the level of confrontation and defensiveness is directly proportionate to how aware that person is of the cruelty that takes place.
But it comes with the territory. I tend to not tell people, and order vegan items from menu's if im out and about or in a group. People aren't stupid, and they will notice your order is different from others.
They will see your non-leather wallet / purse.
They will see that you have asked for soya milk for your coffee/tea.
People will pick up on so much without you even needing to bring it up.
And when they ask the question, that's when I discuss my choices.
Yes, it may be a passionate topic, and people may become defensive, try to belittle you, dismiss you as some kind of hippie do-gooder. But the important thing is that keep true to yourself.
Nobody knows everything, and therefore one of the best assets of this website, and others like it, is its level of knowledge and experience. There are people on here who have been vegan for a LONG time, and they have had every smart ass question fired at them, and you'll be glad to know that for every smart comment is a smarter answer.
Not that one-upmanship is the goal
If you do feel awkward going to restaurants and bringing up the "vegan options" question, then my best advice is to do your research beforehand - I don't mean that condescendingly.
I didn't particularly like asking that question at restaurants either. I tended to overthink the situation and worry that the waiter would "roll his eyes" at me. Silly I know, but I just didn't have time for it.
So what I did was check the menu online in advance. I know its sounds obvious but it really does save time and unnecessary stress.
You do overcome that paranoia eventually though. In fact I have found that as veganism becomes more mainstream many restaurants really hope for feedback.
So yeah, stay strong positive and I wish you all the best. Don't be scared to be announce your veganism, and if people want to criticise you, then arm yourself with knowledge.
All the best