I’ve been exercising for a few months, now. Bought some weights to supplement what I started with, and now I’m wondering if there’s something I’m overlooking or if I should just keep up what I’m doing. I feel better than I have in years, mentally, but I’m also fairly tired and instead of the extra energy I had when I started, it’s tempting to just sit and be vegetable-like on my days off. So…

Monday, Wednesday, Friday:
Front plank for 50 seconds
Side planks (both sides) for 50 seconds
My own patented (yeah, right) version of a sit up that uses the ottoman so I have no back support – 50
Bicep curl – 15 @ 25 lbs. Up from 10 lbs. when I started
Deltoid lift – 10 @ 10 lbs. I’ve been stuck on this since I started
Tricep lift – 15 @ 20 lbs. Up from 10 lbs. when I started
Push ups – 3 sets of 15
Bench press – 20 @ 90 lbs.
Calf lifts – 50 (body weight only)
Side leg lifts, both sides – 50
Front leg lifts – 50

Tuesday, Thursday, Saturday:
Cross trainer machine, set on level 15 (levels go from 1-20), random difficulty profile, for 30 minutes and I try to keep my speed up above 60. I know that doesn’t mean much unless someone has the same model, but 60 is moderately fast – enough to keep me panting and sweating through my clothes, and level 15 lets it get stiff enough that I have to use my body weight to get the pedal down.

My goal when I started this was just to get into better shape, and I’ve done that. I’ve also increased my endurance, I don’t get sore arms when I carry things, and my mental state is drastically improved. But climbing stairs quickly still makes my legs feel tired, and when I’m done with my exercise first thing in the morning, I’d love to just lay down and go back to sleep again for a few hours.

Am I pushing too hard? Should I back off? I tried skipping more days than just Sunday but I don’t get that mental lift when I don’t exercise and I miss it.

In order to know how ideal or otherwise your workout is we would be well served knowing what your aims are.
If you want general endurance, and enjoy training 6 days a week no problem but if you want to build up then you will not be helping yourself.
Biggest red flag I am seeing is nothing to do with days you’re training but huge gaps in what body parts you are training. You are training the limited muscle groups almost exclusively and repeatedly while missing out major muscle groups.
Core work – Front plank, Side planks, sit up, Front leg lifts (Latter 2 heavily reliant on hip flexors so not good for core or abs)
Arms – Bicep curl, Tricep lift
Shoulders – Deltoid lift
Chest – Push ups, Bench press (both strictly speaking have triceps as prime mover so more arms than chest)
Calves – Calf lifts
Leg adductors – Side leg lifts
Back – Nothing, especially an issue with lack of lower back work when doing so much on hip flexors and abs.
Quadriceps – Nothing
Hamstrings – Nothing

In short balance severely lacking, very common for beginners and easy to fix. To get balance use BALS (Back, Arms, Legs, Stomach) or pull, push, legs, core. BALS is easier to remember than PPLC.
Below is an example only, variation is good.
Pull – Deadlift
Push – Bench Press
Legs – Squat
Core – Plank
Pull – Pull Ups
Push – Shoulder Press
Legs – Calf Raises
Core – Side Plank

Variation is good, try to shuffle things up every few months to keep the body guessing, this could be changing exercises, style of session or both.

Too much isolation. A beginner needs more compound lifts to set a foundation of strength. No real legs or back to speak of in that routine. You need compound lifts. Dead lifts, squats, bench, barbell rows, ect. Sure, you can have isolation, but I can tell you from personal experience, starting out with strictly isolation will get you nowhere fast. I can’t really tell you what rep range to work with, as your goals may be different from mine. When I was pointed in the right direction and started with the big lifts, I worked in the 5×5 rep range, which did wonders for me, and will always be my fall back.

Side note – If you’re working out to lose weight, compound work will burn more calories than isolation ever will as you are working more muscle groups with one lift than you are just isolating only one.