I'm not being funny, but after a year of riding I think you should be able to ride 3-5 miles a day, every day, never need a rest and your legs shouldn't ache! We are talking about less than 30 minutes gentle exercise there (or less than 15 minutes of vigorous exercise).
Are you climbing any hills in those 3-5 miles? If so, how long are they and what gradient? How long does it take you to cover 3-5 miles?
You will not be properly warmed up if you just go out and attack flat out from a cold start. In fact, it takes me at least 5 miles to warm up so I would never ride quickly on a 5 mile ride (unless I'd warmed up on my gym bike before the ride)! You'd be better off doing 3 miles slow and 2 miles fast, than trying to do 5 miles fast. Better still - do a 5 mile slow warm-up, turn round and ride 4 miles back fast, and then slow down for the last mile or so to relax your legs again. That would be a nice little work-out which you should be able to complete in under 45 minutes. Once that starts to feel ok, extend your range. But once you start doing longer, harder rides you will need easy recovery or rest days so factor them in to your plans.
I reckon you might well have your saddle too low - follow Keith's advice on that.
I think you might be using too high a gear too. Aim to be pedalling at a cadence (revs/minute of the cranks) of (say) 80-90. Select whatever gear you need to achieve that at the speed you are riding at.
Let us know how you get on!
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