Concerned for lack of baby moments and body aches

Ladies I’m 20 weeks pregnant I just had sex yesterday after a while maybe a month or more since not having it . He came inside me . Idk if that was a good thing to do but I forgot that sperm can cause contractions. Later on in the night my lower back started hurting , and it felt like bad period cramps . I know it’s too early but I’m like what if I caused an early labor, today I wake up my whole body hurts. I don’t remember feeling this with my first . But now I started being concerned because with this baby movements are hard to detect and from what I remember I don’t think I’ve felt baby move today, decided to lay down and see if I can feel something but so far not much. I haven’t had consistent movement with this one so I’m trying not to worry. Has this been normal for anyone ?