I've been a Junior Mens racer for nearly a year now but have been commuting for nearly a year and a half. My current bike is a 1972 Schwinn Sprint and my race bike is an upgraded Specialized Allez Elite. (I am the only person in my school who owns a road-bike) Next year I will be commuting to a different school. My current commute of 1 mile is not exactly difficult and primarily covers residential neighborhoods. However my commute will increase to 3.5 miles. This worries me for several reasons
1. I can't sustain more than 15 m.p.h. on this relatively short commute due to the weight of backpack and bike
2. I'm out-growing this bike
3. My back hurts like heck from the back-pack
4. Commute takes 3 minutes currently and I like arriving half an hour early. Arriving on a timely fashion would necessitate leaving at 7:00
5. This bike has had three serious mechanical failures thus far including loss of all brakes and 2 chain incidents one which caused me to crash and another leaving me stranded in traffic (I had to push amidst cars which was potentially dangerous)

I believe I need a quicker bike. Some constraints:
-Budget is $150
-Bike must be capable of 17 m.p.h. for the duration of the commute
-Must be a road bike
-Should Have provisions for rear panniers- about the panniers: Is it possible to purchase one which will accommadate a backpack and it contents as well as a change of clothes and the like (I'm fine transferring books back into pack if necessary)
-There is a fair sized hill; not a problem on my specialized but I'd prefer not to walk

Any recommendations for panniers and bike?

I'll wear a cycling jersey and Cutter-tech shorts and change at school to avoid sweat issues...
Should I purchase lights, reflective gear etc?