Well….I wish I had a magic formula, but it took me until I was 33 to break past the 3-mile barrier for the first time. Everybody is different, but for me I just had to force myself past 3, and then when I got to 4 my body started to relax and I got into a rhythm. Even now, the first three miles are always tough for me, but I start feeling better when I get past them. This is one of the big reasons why I still do a 1 or 2-mile warmup even before a full marathon.
Don’t worry about the differences in pace on different days. It is normal to have good days and bad days. My advice is to listen to your body. If you feel OK after 3-miles, keep pushing. If you push past 3 and still feel bad, stop. Stopping is always OK. There are many days where I have a set distance planned but stop early because it just isn’t my day.
Another thing that has really been a help to me is running with a friend. I don’t know if this is something you already do or not (or if it is an option), but it has been a really big help to me. I helps to take my mind off of the miles and just enjoy running with a friend.
The important thing is that you are out there giving it a shot. For that you should be proud. Keep running, and feel free to shoot a question anytime if you need some help….Tim