Alcohol & Drugs: MIP, MIC, Intoxication Public Intox in Texas

[bigfully]

I was arrested for PI last week. I had a flat tire and pulled over to fix and I couldn't find the tire tools. I had a few drinks earlier but several hours earlier. but decided to relax for a bit and fell asleep. When the officer knocked and woke me up, I was caught off guard and he immediatly wanted me to do a field test and I refused saying give me a minute. He put me in cuffs, and off to jail we went. I then passed field test in processing, with comment from officer " why didn't you do it 5 minutes ago" ... anyways my question is do I need a lawyer, I have a previous DWI.. will this affect, can I get jail time or probation. I heard this is only a fined offense. Can I plead not guilty, seeing how there is no proof of intoxication, (only smelled of alcohol)?