Hello and welcome to eHealth Forum!

If you had sex the day your period stopped then in all probability you cannot be pregnant. The symptoms that you have (sore breasts, lower back pains, cramps, peeing a lot, feeling nauseous-especially in the mornings, feeling tired) can be due to ‘honeymoon cystitis’. Generally first timers get a UTI called honeymoon cystitis. Trauma to the genital and the urethral orifice, and bacterial contamination from the fingers or mouth of the either partner makes cystitis prevalent among honeymooners (first timers), especially among females.

Drink plenty of water, cranberry juice when symptoms start and follow good personal hygiene before and after sex like bathing or washing the private parts well will help prevent it to a great extent.

Since a confirmed diagnosis cannot be given on net please discuss these possibilities with your doctor once. Hope this helps. Take care!