I was thinking about[of] ~ 할까 생각 중이었어

I was thinking about studyiung Geriatric Psychology

I was thinking about [of] you

I was thinking about [of] switching my major to Business

I was thinking about [of] talking a trip overseas

I was thinking about [of] moving to Canada

I was thinking about [of] creating my own online course

I was thinking about [of] going back to school

I'm thinking about joining the Air Force. Any advice?

I'm worried that you might be dispatched to combat zone 

참고 서적 : 영어회화의 결정적 패턴 (www.yes24.com/Product/Goods/74400061?scode=032&OzSrank=1)