Training should always be FUN - if you don't want to be there mentally, then maybe it's just not the right thing for you to do.
When I was doing JuJitsu, I started 2x per week at my college (that's where I met my sensei), and later on he invited me to train at the dojo as well. For about 6 weeks or so, I was going to the 2 college sessions *and* the 3 days a week at the dojo.
Yes, that's a heck of a lot of training, yes it took its toll on me (I ended up hurting my shoulder and had to sit out for nearly 2 months), but was it FUN
? You bet
There were lots of times during that period that I was saying "Geez, I just went to train yesterday, now I gotta train today too??" (Of course I didn't have to, but as soon as my brain got past that, and I was driving to the dojo, I knew it would be ok.)
There were other times where I'd have an awesome time at class one night and the next day I'd say, "I just went to class last night, I can't wait
to find out what I'm gonna learn tonight!"
It's all in your mind - if you enjoy what you're doing, you'll find a way to get there. If you don't enjoy it....REALLY don't enjoy it, then don't waste your time.