I was where you are this time last year, today I had an evening run of 42 miles @ 16mph, I hated hills with a passion, but kept at it through the winter, struggled with speeds through Feb and March and then finally in April my speeds and stamina really started to improve, my first ride was 8 miles @ 9.32mph.
Use an easier gear than you think you should be in (or two) and try and keep you pedalling speed higher, this makes it easier to actually pedal, the increase in the pedal rate (known as cadence) will help keep you speed up, this will take some time to achieve, but practice gets there.
Frequency of rides if your body legs ache, rest them till they dont (usually 2-3 days if really bad), this time allows the body to repair the damage done during exercise, when the body has repaired itself, you will be stronger and fitter, again it will take time to see an improvement, but keep at it, it gets better.