I agree to Naoki-san. As you and others say, ちゃって is from ちゃう, and ちゃう is the casual way to say てしまう. I suppose there are two usage for Vてしまう: 1) to V **in an unexpected way**. ≒ You cannot control to or not to do so by yourself. 2) to V completely ≒ to finish V-ing. Now you might guess usage #1 will be adequate to 考えちゃって. I’d say 一人で考えちゃって means like “I cannot stop thinking to myself. I do so without intention.” Additionally, I don’t think ちゃって is a feminine word, but just casual and like conversational. Men can also use it. But try not to speak with long えsound at the end like: ちゃってぇ～, that is feminine, more like childish, or add suffix ね or さ at the end ～しちゃってね／～しちゃってさ; good for both male and female. e.g. 最近彼女のことばかり考えちゃって。 Well, you might fall in love with her!?

”ちゃう” is the casual way to say "てしまう". Usually you give negative conjugation when you say "てしまう" or "ちゃう". You probably know the meaning of "一人で考えちゃって". The conjugation of the sentence is like he/she is super serious person and always worry about something like "what if this happened...". You know those type of people right?? lol

It means "I thought about it" ちゃって is a feminine way of speaking and is informal for 〜てしまう