Worried about dehydration— has anyone used home hydration test kits?

I’m experiencing a lot of muscle pains and brain fog that I’m pretty sure are a result of lisdexamfetamine (I’m in the UK and taking Elvanse — I don’t think vyanse is an option on the NHS). I’m pretty sure this is due to dehydration. (Granted, it could also be perimenopause, PMS, or the interaction between the lisdexamfetamine and the lamotrigine 50mg and fluoxetine 20mg I also take daily, but I’m aware that these too can have a dehydrating effect). I have had blood tests done every few months at the gp and they always say my electrolytes are fine but that’s just a snapshot at that moment, right? So I was considering buying a home test kit to test my hydration levels when the pain and brain fog flare up. Has anyone else done this?