What Causes Uterine Cramps With Pregnancy Symptoms?

Hello I had my last period on 20th of August n I has sex with my husband a day after my period n on 10,12,14 and 16 of my cycle after 2 weeks I had all the pregnancy sign then on day 28th of my cycle I felt a crump under my tummy for 6days the day 7th I has my period with no pain n today I felt something stony in my in my womb I don t know what is that thnz