인생 all of my life, like from birth to death. 생활 is life to live. Way to live. 생활이 함들어요 means nowadays coz of money or friends,its not easy to maintain my life, 인생이 힘들어요 means my life (from birth to death , or could be destiny) is too tough.

What Sujin said. But, for exaggeration, you can say "인생이 힘들어요." to mean "생활이 힘들어요." Also it's useful to know that "인생이" often collocates with "고달프다"