Bullhorn or drop bars will help you out alot on long rides. I find after riding about 90km the non-stop pedaling of a fixed gear tends to make certain unfortunate areas go numb so its best to take a little break off the bike every now and then. Riding no hands for a little while is a chance to stretch your arms back and neck. I don't think theres a reason to get a new bike... The longer the geometry the better, but best to work with what you have and get new bars and stem. You just need to keep riding and your body will condition itself. Make sure to stretch (I never do ... but I should)