I encountered a lot of difficulties when I was studying abroad.
While I was studying abroad, there were some difficulties.
留学中 = while studying abroad
大変なこと = troublesome things
たくさんあった = there were a lot of
面接で、二つの言いたいことがあります。これらを接続するため、even though または although を使えます。
Although I had some difficulties when I was studying abroad, I hung in there.
I hung in there even though I had some difficulties while studying abroad.