I thought I'd explain my point in an answer. Grammatically speaking, it's not wrong to use an exclamation mark, and in this case, I think it's a matter of style, communication and personal choice.
Style: Using an exclamation mark means you're emphasizing what you just said, and this is easily achievable putting it where you need it, but what about formal writing? I suggest not to abuse, or better... I'd suggest not to use exclamation marks at all in formal writing. There are better and less invading ways to express the same thing using a formal style. It's not your case since Tweeter is not really a platform where you write "formally", but I wanted to cover all points.
Communication: If there is no style matter, i.e. it's an informal writing, then the question would be: what do you want to communicate? Like I said in my comment, the point is: if you want to emphasize what you just said, use the exclamation mark, if not, don't. Although it's informal, still try to avoid abusing it, because the more you use them, the less effective they might appear, not to mention you'd be risking to just annoy the reader.
Personal choice: In the end it's you who decides whether to use an exclamation mark or not, but keep in mind that a language has rules, any language, and not only for grammar, but also relating to communication and meta-communication. If you follow those rules, you'll be fine.
TL;DR: No, you don't have to always use it, it's not a requirement in most cases. Then, it depends on the situation, sometimes you can use it, other times you must not use it.