so actually the walk ( done briskly as OP gets fitter) combined with a short weights routine, should make a difference
Only if the OP walks so fast she is slightly out of breath.
The thing is, even those of us who are pretty fit, started once! The times when I have been following a programme and the next step up makes me feel broken, the first time I do it. It's a matter of gritting your teeth, and doing it. And doing it again.
OP you need to set goals that are achievable, and get balanced between being too hard, leaving you exhausted & sore & demotivated, and too easy which don't really increase your fitness.
This is where it might be worth investing in a PT package - generally you could purchase say 4 or 5 sessions, for once a week, to get you going, then they'll give you a programme, and you could check in once a month or so. A good PT will be a coach, a psychologist, as well as a fitness guide - they'll try to work out how to help you motivate yourself.
Bodies adjust - we are all naturally lazy - bodies adapt & find the easiest way of doing something. So you need to find the moment of challenge. As you get fitter, you can train to failure - that was the hardest thing for me - to start to see failure as the next training step.
As a PP says upthread, if you're doing say, 8 repetitions (reps) of an exercise, the last 2 or 3 should be really hard. Not impossible, but they should cost you something.
Then you take a rest gap, and try again.
It's those last 2 reps that get you fitter! They are the body responding to the extra exertion you're asking of yourself.
That's why Couch to 5K is so good - it's programmed so that you can just about do it (I always get stuck on about week 5, and have to do it 2 or 3 times) but it also pushed you a bit.
And the advice for C25K always is - if you're so exhausted from the exertion you feel sick, go slower.
Come on over to the Exercise forum @worriedaboutfitness - you'll find LOADS of good advice & fellow exercise-dodgers!