You say you have been "slacking off big time" and are "tired of plateuing." To me, these two statements conflict. In my opinion, plateauing means that you have been given a consistent effort toward a goal and despite this effort, progress has stalled. This does not seem to be the case with you according to the first statement. You are not plateauing, you have been, perhaps, unconciously, maintaining. Doing just enough to keep from gaining weight. This is not a bad thing at all. In fact, sometimes taking a break from the weight loss battle is a very good thing. The best thing is you have found your maintenance level and to resume progress to your goal, you just need to create a caloric defecit from that level. It can come from either reducing your caloric intake, increasing your caloric expenditure, or a little from both.
The fact that you have halted the aerobic exercise routine that you had previously done shows that it was not yet fully ingrained as part of your lifestyle which hints to me that either you really did not enjoy it in the first place or you were bored with it. I believe that's where the key lies. Keeping it fresh and enjoyable.
Have you tried interval training?
When you did your 30 minutes, did you just do 30 minutes at whatever pace came naturally that day or did you record your distance/resistance levels and aimed for progression?
I would suggest doing 2 days of HIIT on your favorite piece of equipment, and then do 1 "personal record" day on each piece of equipment. (3
PR days total) Do your 30 minutes but try for personal record. You could measure by distance or by the machine's theoretical calories burned. Each time you do one of these personal record workouts, it is a contest in which you need to beat your previous best distance/calories burned.
At least for me, When I am just "putting in my 30 minutes of cardio" the clock can seem to go excruciatingly slow and the 30 minutes seems to last forever, but when I am racing the clock, trying to establish a new record distance, that clock seems to speed up on me.
I would take at least one day totally off from cardio, if you want to take two days off that is OK too. If you just want to do a sixth day, I would either do another
PR day on one of the machines or just do a day where you get on any machine or multiple machines you feel like and go at whatever pace you feel like for as long as you feel like, whether it is 5 minutes or 2 hours. This is an "anything goes day."
Hopefully, these ideas will help keep things fresh and enjoyable.
As for the resistance training, other than to say, by all means you should be doing it, it is hard to make any recommendation beyond that because all we know is that you have dumbells but don't even know if it is 2 dumbells of equal weight, adjustable dumbells, or a set of dumbells. Knowing exactly what you have, would change the suggestions/ideas dramatically.