There are a lot of really short core workouts here. You can do as little as two to five minutes every morning & night and still notice a difference. Core work is great for health and stamina. Not so great for weight loss or trimming the belly. For that you need calorie burning exercises like cardio, HIIT, or bigger compound muscle exercises.

Here are some little core workouts to start with.  I recommend searching for more and keep changing and trying new ones. It doesn't matter if one is "too hard" what matters is you regularly push yourself just a bit past your comfort zone. I do the 5min planks workout regularly and i still can't hold them all for the full minute. Getting better though.
Lil' Bunches O' Crunches 2:00
3min Abs 2
4min Abs
5min Full Abs
Planks 5:00
Cardicore Tabata 4:00

Good luck

if you dont like to exercise, i think yoga is the perfect thing for you! its never overly hard where you are dying and cant breathe, but its great for toning and shaping and gaining strength!

theres tons of beginner yoga workouts on YouTube, i think you might really enjoy. do it everyday for a week, i promise you you will find you are stronger in your upper body!