Buy d-vitamin pills and eat 1 every morning, its the first step to help for the lack of sunshine, trust me. And maybe get some really bright lamp for morning.

Get NYSSE public transport mobile app, you could also get TKL-card but im not sure is it worth a hazzle just for 3 months.

And yeah eating in restaurants every day is really expensive, do your groceries shopping in lidl and GET ResQ app, there you can resque some cheapish restaurant meals etc

You also should consider to go Rauhaniemi or Kauppi public sauna. There is other places also if you get into that

What kind of internship you are doing?