“You seem forced” can be used to indicate what you’ve expressed
Your meaning may have been gotten better than you think. “You seem forced” employs a fairly common usage of “forced”, indicating strain even though there is not a physical force. Note that “you look forced” in your question’s title is a little different, having to do with the way that “seem” refers more comprehensively to apparent behavior and “look” refers more to physical appearance.
Another way to say this that would be specific to tone of voice, diction, etc. would be “you sound forced” which could be hedged a little as “you sound a bit forced” and would be helpfully followed by a bit of explanation or a question, such as “is everything OK?”¹ or “do you feel you have to talk to me?”
Expanding on the “look”/“seem” difference in “you don’t look yourself”
With “you don’t look yourself”, it seems like you are saying that something about the other person’s physical appearance is unusual compared with historical data or some assumed expectation (e.g. someone’s face is green or streaked with tears and you assume they are not always that way, even if you don’t know them).
If you were to say “you don’t seem yourself”, your comments would be understood to refer to someone’s overall presentation. This could certainly include physical appearance, but is more often used to refer to someone’s speech, body language, and other aspects of behavior. I believe this phrase would fit the situation you described.
Note for “you don’t seem yourself”: Similar to “you don’t look yourself”, you would be understood to either be making a comparison to ways you’ve seen this person act before or ways you assume they normally act. For example, you think that the person doesn’t normally put so much emphasis on their words or deliver them in a staccato rhythm.
The note from the end of §1 of this answer applies here as well. Since you’re guessing at something about another person, it probably wouldn’t be a bad idea to describe a little more what you mean by what you’re saying. I personally think it would be appropriate to ask a question aimed at learning more about how this person is feeling and/or what they think about the situation.
Your attempt is not far off - just a few grammar errors.
While you could say:
I'm here to learn, that's why I asked so many questions - even if it looks stupid. But you were harsh.
I'd recommend to change the last part:
...But I think your comment was too harsh. or
...But your comment hurt.
The reason:
The person you are talking to might feel attacked if you say something along the lines of "you did XYZ wrong". Especially if the discussion went for a bit or is heated / emotional. If you state how you feel or percieve the situation, the other person can't argue about your feelings.
Best Answer
I understand and sympathize with your concern.
First, it is very important for you to understand that in English, unlike in Chinese and many other languages, we do not have different "ranks" or "grades" of personal pronouns. Ours is a very "egalitarian" or "democratic" language where pronouns are concerned! The second person pronoun "You" is neither respectful or disrespectful, and no-one will think of you as impolite if you address him or her as "you" in English.
Here at the English Language Learners site, you do not need to express your thanks before you receive an answer. The people who answer questions here do so because they enjoy it, so you do not need to thank them before you have an answer.
If you ask a question and you do receive a helpful answer, the best way to express your thanks is to click the "Accept Answer" link. This will raise the reputation of the person who helped you, and they will appreciate your response.
In answer to your specific questions:
#1A. See above!
#1B. In English, the word "someone" is not at all disrespectful. If you write: Can someone answer my question?, that will be perfectly polite and sufficient.
#2. "Grateful" is a very good word to use when you are expressing thanks. You could also say "Thankful."
#3. See James K's answer, and my third paragraph above. Your gratitude is welcome and appreciated, but you don't need to express it before you have an answer!