Still Running but what am i doing wrong?

So I have stuck with my running program pretty well.  Yesterday the schedule said I had to do 5 miles - 5!  OK I know for some people this is probably a breeze but for me this was tough.  I was already tired from a long days work.  I was dreading the treadmill and I refuse to run outside in 15 degree weather.  I finally sucked it up and went to the gym.  I wasn't going to allow myself to skip out. 

What I want to know is why is there a 5 mile run on the first week?  It seems like a lot, especially since I'm just training for a 10K.  I couldn't run the whole thing and I didn't want to push myself since I have 7 weeks of training left.  I walked the first mile to warm up.  Then I started running.  The first mile is always the toughest for me.  If I can make it past the first mile I'm usually OK for the rest of it.  While running, I can feel a blister developing on the inside of my foot near the arch (what little arch I have - my feet are pretty flat).  It hurts pretty bad but I push through.  I walk the last mile to cool down.  Finally I'm done.  But I'm not feeling great.  I'm tired and my body hurts.  My ankles are sore and my knees feel funky.  I am doubtful that I can make it back to my apartment and into the shower.  Somehow I manage.  After the shower, I fall into bed exhausted. 

One thing I can say for all this running:  I am not drinking alcohol as much.  1) I feel like its such a waste to go run only to add the calories back on with liquid 2) I just don't want alcohol in my body - I am actually craving more water. 

Here is my problem:  Running does not seem to be getting easier...and I have never had a runners high.  I trudge through it, finish, and limp back my resting spot.  Is there something I'm doing wrong?  Is there something I should be doing that I'm not?  Could it be I'm just not a runner? (this is highly likely)  5 years ago I could get up off my couch and run a 5K realitively easy.  Is it just that I turned 30 and my body is giving up?

Today the schedule says 4 miles.  My body says no but the schedule says yes.  Off to the gym I go...