Stretching!

Hey wonderful mfp people! So I'm on a mission to lose 110 more lbs to get into a regular BMI, I've tried and tried in the past and ive never followed through with dieting, so I've started going to the gym this month and I absolutely love it! Today was my 7th gym visit, and I'm starting to feel a bit sore in my sides and lower back, I do mostly elliptical, bike, and treadmill,, and I do stretch half heartedly after in the change room but I don't really know what I'm doing and considering I'm 110lbs overweight some YouTube stretches aren't realistic for me, so I'm hoping someone can help and suggest good proper stretches post workout :) Thank you!