Re: What happens when I go home?
Definitely agree with the journaling suggestion. Make a note of things like how you feel, too, both physically and mentally. The first step to identifying a source of stress is noticing that the stress exists.
There are two things to consider if you're tempted to do any kind of conditioning outside of class. First, could you be at the dojo during that time instead? Especially at the beginning, there are so many new movement patterns to learn that more time at the dojo will almost certainly do more for you than non-aikido-specific training.
And second, will what you are doing help or hinder your aikido? You might want to consult your teacher about specifics, but for example aikido places a premium on body mobility. So do yoga and dance, but strength training often does not.