"I was thought ..." is the passive voice. For example "In those days, I was thought to be a great hunter." That is to say, "In those days, people thought I was a great hunter." If you say "I thought," it normally means you suspected something, but now you know it's not true, or you have reason to doubt it. e.g. "Hm... I thought I left 6 eggs in the fridge, but now I see there are only 4." If you say "I was thinking," it normally means you were considering something. "I was thinking about whether we should go to Disneyland this year."

I was thinking... Past perfect continuous. I started thinking in the past and continued to do so up until a specific time. It is not a complete sentence because it needs a time frame and an object or just an object. Example: I was thinking about it all last week. I thought. Simple past. I had thought. Past perfect. I was thought. Wrong.

'I was thinking' is correct, also 'I thought' - without 'was' is correct. (past perfect tense)