You REALLY need a thermostat, or a dimmer switch now. Your cool side temperature is good, maybe a little lower (down to 76 or so), but your warm side ambient and basking spot are WAY too high. Your ambient temp should be around 82-84 with a basking spot of about 88. Your temps are too high for any boa, and you have an Argentine too, they are from Southern South America where it's even cooler and sometimes a much higher elevation (so again, EVEN cooler) than most of the other boa constrictors, hence the somewhat lower temperatures I listed above.
Go out and purchase either a thermostat or a dimmer switch first thing today, this is not something that can wait. I hope this pic shows up...
. That's what I use and I LOVE THEM. You do not have to splice any wires, you just plug your heat source directly into the back of the plug and slide the dimmer switch to adjust the output. If you buy it (try Home Depot or Lowes, etc..), plug it up and test it out and measure your temps with something VERY accurate like a temp gun and you can adjust the temps with the slide on the dimmer switch until they're perfect.
Now, after you get your temperatures in order, you can worry about feeding. This problem may fix itself after the temperatures are stablized, or, it may fix itself after breeding season. Boas often times go off of feed at this time of year because it's the natural time for breeding season, and you just have to wait it out. Normally, they don't lose any significant amount of weight, but it's quite possible that yours did because of the very high temperatures. I would say as long as your boa is not looking sickly, you have nothing to worry about. However, given the conditions it has been kept in, a trip to the (qualified reptile) vet wouldn't hurt.
Good luck GP and like I said, do NOT wait or hesitate to buy a thermostat or a dimmer switch, do it today!
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Jonathan Brady
My Kingsnake Photo Gallery