It's completely normal to feel whatever way you feel, and that includes angry or drained or sad or any other emotion - or a mix of them.
I had a similar diagnosis, high grade DCIS, but slightly different treatment; I had the lump removed, but no radiotherapy because I'll be having a double mastectomy.
Even if you get the "good" news that "it's only DCIS" (I had a couple of meetings with a surgeon who kept using this phrase, and I wanted to slap him, seriously :s ), it's still a huge upset - suddenly your focus is wrenched away from your regular life to dealing with this thing that just landed on you. You're trying to juggle work, family, friends like usual and then add in medical stuff, which can be unforgiving in its scheduling, all with the spectre of cancer hanging over you.
And yeah, it often feels like nobody else understands exactly what you're going through.Even other people who've been there - I have a colleague who's had a similar diagnosis a few years ago, and she's lovely, but she's insisting that, because things went a certain way for her, I'll follow the same path - and it's not so.
I don't have any guidance or advice except to echo @Jenmcd above and say be gentle with yourself I hope you click with your psychologist and that they're helpful for you. I hope you find space for your thoughts and emotions, and comfort for them and yourself.