Fighting Bad MoJo in The Pool

I'm an overweight 52 year old man who has made a somewhat miraculous return to swimming. I've been swimming 4 to 6 times a week for about 12 weeks now. My workouts began with 9 x 50's the first week and have progressed to about 1800 yards in about 50 minutes (typically 2x450's, 200 kick with fins, 5x100's free, pull or paddles, and 4x 50's). I had a swim buddy but he finally decided that he just hated getting in the pool so he quit on me. So I found a small group of Masters swimmers at my club who swim early morning at 5:15 AM and I joined them this week because I find it very difficult to stay motivated swimming solo. When I showed up this morning no one was there, so I jumped in and started swimming. I had ZERO MOJO, didn't want to be there, the voice in my head was screaming quit, quit already. I felt tired and lazy and barely managed to finish a sloppy 1500 yards. I've felt this way in the pool before and I think it's how my buddy felt and why he quit. Does anyone have suggestions as to how to fight this feeling some days and how to stay motivated and determined everyday you go to swim? I mean it's 5:00 AM and you're already there, why not just bust it out and finish your workout. Thanks for listening to my personal appeal for help.