I had my last period on the 5th of July and had unprotected sex on the 12th. I have been feeling very sick the last few days and have cramp like pains in my stomach and lower back. How early do symptoms start and would the start sooner if I were pregnant with twins?

Symptoms usually start around 4-6 weeks a suppose they could start earlier but I doubt that early.Im not sure about the twins bit.

You might start feeling some changes early on... some women will even before they miss a period. With twins, hcg levels are higher, so you may indeed experience some symptoms sooner or in greater discomfort... but it doesn't necessarily mean twins.

As Holly said, many women don't feel any symptoms for quite sometime. It is very individual. Not eveyone will experience every symptom or at the same time.