What is wrong with my 2006 Volvo S80?

What is your question?

Possibly lengthy post with a variety of issues. Bare with me as I know nothing about vehicles. 1. My headlights keep blowing. I just got the notification that my left low beam is out again. Why does this keep happening? And I am on my way to purchase another bulb but I have no idea if this Volvo takes halogen or HID. 2. My heat barely works. In the summer the heat works fine. When it's warmer out, the heat works fine. As it gets colder, however, it stops working as well. Anything below 35 degrees Fahrenheit and it barely blows air out. The air that does blow out is luke warm at best. Maine winters can be harsh and this hasn't been fun. I spent upwards of $1,000 last winter to get it fixed and it still doesn't work, and no one seems to be able to understand WHY. 3. My check engine light came on about 8 months ago. I got my oil changed at Walmart. They seemed confused as to how to change the oil on a Volvo, and I'm not sure if this plays into it but as soon as I left...