Ah, I so know how you feel. It sucks when you have a really good week and then you don't lose much or have a gain. The best thing you can do is just put it behind you and keep going! Are you making sure that you're eating enough for your body to sustain all of the exercise that you've started doing? Perhaps you're not consuming enough calories now and your body has gone into survival mode and is trying desperately to cling onto what fat it has. You could try having a few extra healthy snacks, like yogurt and nuts etc.
Also, it's completely natural for your weight to fluctuate day to day. Try not to focus too much on the daily scale readings. I know it's easier said than done, and to be honest, I'm a compulsive scale checker! I often weigh myself up to 3-4 times a day to see how I'm going. However, I weigh in "officially" once a week and that's the only result that I really judge myself on. If I have a loss during one of my unofficial weigh ins, I use that to motivate myself to keep going. However, if the scale shows a gain, I just shrug it off and think "well, that one didn't count, it wasn't official!" and then I just make sure that I'm eating as well as I possibly can be. Funny how the mind works, isn't it?!
Usually after I have my official weigh in on Sunday, I usually make Sunday my cheat meal day and go out and have sushi. It's not uncommon for my weight to bounce back up the next day, but it generally settles again by the next official weigh in. TTOM can really mess with your head and the scales too, it's quite normal to notice a gain around that time, as your body naturally retains fluid.
You're doing really well so far and I'm sure you'll be back in the 80s again soon. Keep going! Did you end up going to talk to a doctor for their advice?