Sore Throat after Practice?

I just started with 30 Day Singer and I have the self-taught problem where I'm comfortable with some intermediate topics (vibrato, ear training, mix voice) but not comfortable with some basic ones (mostly breath support, maybe others?), so I'm starting with the beginner 30-day course. Because of this, I'm kind of going through the videos as quickly as I can instead of day by day, mostly because I feel a lot of them are review. I've been doing this for 3 days and so far my schedule has been

1) Do the Warm-Up in lesson 2
2) Do a few daily lessons until I feel I've reached something I need to practice more
3) Go to bed

In the past 3 days I've gotten through 16 lessons but when I wake up in the morning, my throat just feels somewhat sore, kind of like after a workout. There's also a little bit of hoarseness that goes away as the day goes on. It doesn't hurt to speak, sing, or swallow, I feel fine when I practice, and it's a very low level of pain, but I'm wondering if I'm doing something fundamentally wrong. Is it normal to have a small bit of pain when starting a daily practice regimen (there are muscles involved in manipulating the vocal chords, right?) or am I doing something that introduces tension?

Reviewing some of the other posts about vocal health, I realize one of the problems I'm having is that I'm not drinking any water during practice, which is almost certainly causing more strain than is necessary, and I'm on an ibuprofen regimen for an injury, which might not be ideal but there's nothing I can do to change that. 

I think the ways I'd like to improve this are:
1) Take a rest day today to focus on ear training or other kinds of listening exercises
2) Vary the warm up with other ones from the YouTube channel (this isn't really for tension reasons, but I think it'd help me make sure I do a warm up instead of wanting to jump into new lessons)
3) Make sure I have water on hand when practicing!
4) Possibly incorporate cooldowns into my daily practice? (I found this on the YouTube channel which seems to make sense for this purpose? https://www.youtube.com/watch?v=bMQx8rDPSVc)

Please let me know if this makes sense or if there's anything else I should be doing to improve or if I'm over- or under-reacting!

That sounds like a great plan, Rosella! Even if you're not doing anything to cause strain or excess tension, prolonged voice use can still cause fatigue and swelling. I think your instincts are spot on: hydration should make a huge difference, in addition to rest days, variety and cooling down. You might also consider shorter practice sessions, if those changes don't make a difference. 

Have fun!