Should I feel more tired

Might be a silly question, don't roast me. I recently started swimming again, going about 1 mile or so in 50 ish minutes. I alternate breast and free. I'm just not tired at all during, or out of breath, I feel like I can swim forever, I just stop because 50 minutes feels like an adequate workout . Should I be swimming faster? Or is this just a nice workout and I should be happy? I think I have a pain is gain mindset...