Give yourself some time between rides. Hydrate. Drink lots of water. I've found that if I drink plenty of water that I don't have sore muscles or pain at all the next day. And I mean alot. Do some mild stretches before riding to warm up. Back pain could be do to riding position. Change your hand positions or fiddle with seat height, bar height, etc. That often helps solve mysterious pain.
Keep on trying. I've lost lots of weight through cycling. I'm quite proud of how if you change your outlook, you can change your life. Don't give up.
"Things look different from the seat of a bike carrying a sleeping bag with a cold beer tucked inside." ~Jim Malusa
2009 Trek 520-Brooks B-17 Special in Antique Brown
2010 Surly Long Haul Trucker-Brooks B-17 Standard in Black
1983 Fuji Espree Single Speed-Brooks B17 British Racing Green