I was feeling a little under the weather on and off for about 2 weeks before going in to labour. Felt much more tired than usual too, but I hear a lot of women get a big burst of energy before going in to labour. So as others have said, it does vary from person to person.
When I was pg I was always wondering if the belly ache was an early sign or the nausea....but you will know when your in labour. My waters went without contractions for a few hours. I can only describe contractions to be like the cramp you get in your leg.... you feel it come on, hurts for a bit then dies off again. They gradually become more painful but you will know when it happens. I didn't find them overly painful either, I was almost fully dialated before I had my c-section (was an emergency) so I went through about 16 hours of labour, only had 4 paracetamol throughout the whole day.