Breaking the Mile / Breaking 3

The first mile is always the hardest for me. It feels like my joints take forever to warm up, but after the first mile or so they get to going and i don't feel so bad. Does anyone else feel that way? This morning I woke up and ran 3+ miles. The past few times i have ran, I have ran for 3 miles strait and stopped. Which is good don't get me wrong, but i need to push it further. I think I need to shoot for 4 or maybe 5 miles to get past the 3 mile mark. I think i have a mental block in my head saying you are going for 3 and then you can stop!!