Dude, you just phrased it perfectly. I didn't lose as much weight as you (I lost ~60-65 lbs), but I have been in the same boat a couple times. It's like, you work so damn hard to lose the fat that when it starts coming back, it freaks you out, yet that doesn't necessarily get the motivation back. ...and then you start to wonder what it would be like to eat semi-unhealthy like people you know, but instead of automatically gaining weight, you just stay the same (like other people). At least...that's how it is with me. And then you dwell on that and get even a little more in the dumps.
I had a very similar thing happen to me. I started running like a mofo at around the point where I had lost most of my weight. For the next six 8 months I ran a lot. I went from not being able to run 2/3 of a mile without stopping to running a half marathon. It was awesome....and then my motivation died. It just, stopped, for no apparent reason. I gained around 8-10 pounds back and got in a similar slump that you're in.
Then after a little while of doing very little to no exercise on a regular basis, I started doing a lot of body weight exercises. I had a routine that incorporated burpees (google this if you're not sure what it is, it's the single best overall body exercise there is that I've found), pushups, crunches and lunges as well as 'core strengtening' exercises (specifically, the first two sections with pictures here:
Core Strength Training - How to Develop Your Center of Power ). It worked up a routine of around 30 minutes of pretty high intensity (I know because I feel like I'm going to pass out and I'm sweating bullets).
I did that for a while, and got kind of tired of it too. I lifted some weights and did around fifty bajillion crunches to lose all my weight...so yeah, there was a point where I was just burnt out on like damn near all exercises (except for the occasional team sport exercise, which is always fun). However, I started mixing it up and it's been good ever since. For instance, I'll run one day, do my body weight exercises the next, maybe do nothing the next, then do weights and cardio at the gym the next day followed by two days of running followed by the body weight exercises, then rest a day or two, and so on and so forth. There are definitely days when I don't feel like doing anything. Some of those days, I just don't do anything, but some of them I end up doing one of my three workouts.
Yeah dude, I feel that I have been in your same boat with regards to being burnt out on various exercises. However, having three very separate and distinct workouts has been extremely helpful in terms of not mentally burning myself out on anything. I would really try this approach out, because it's worked very well for me. And on top of that, I'm in much better total-body shape than I've ever been in either when I was fat and lazy OR when I was just working like a madman on either of my particular three workouts. Mixing them up = better variety + better fitness.