避けられない means "inevitable" e.g. 死は避けられない This word is usurally used on a formal situation. どうしょうもない means "It can't be helped" or "There is no choice" It is the same as しかたがない、しょうがない But we use しかたがないor しょうがない　more often. いかんせん means "unfortunately" e.g. 新しい車を買いたいが、いかんせんお金がない。 But we rarely use this word because it's rather old. よんどころない This is also a very old word. I have to check it in the dictionary. And I've learned it means "やむをえない” やむをえない　is the same as しかたがない、しょうがない But I think やむをえない is a little bit more formal than しかたがない、しょうがない And you can use やむをえない　as an adjective. e.g. やむをえない理由で行けなかった We don't say　しかたがない理由で行けなかった

What you are looking for is しかたがない or しょうがない

まあ、必ずしもですね。

You already got an amazing answer from Kazumi-san. However, since you seem to ask a lot of high-level questions, might I suggest writing some of them in Japanese? From my experience using italki, you tend to get more and, more often than not, easier to understand answers. If you write your questions in English it seems like you want an explanation in English so very few Japanese native speakers will be able to help you. It also causes misunderstandings for English speakers who know some Japanese like Jace and just wanted to help. (外国人でも日本語の文法分からなくてぺらぺらしゃべれないというわけではないでしょう）