Single Mom Struggling with Sexual Urges

I'm a stay-at-home mom to my six-year-old. We live together and it's great but there are days when I feel so... lonely. The other night, I was in bed reading before sleep and suddenly all these thoughts start rushing through my head. Imagining someone being here with me, making love. It felt like an addiction or a craving more than anything else. My heart races just thinking about it now. There are moments when I feel guilty, am I not good enough for anyone to want? Or is this normal? Is it wrong to fantasize and yearn for closeness like that? Am I weird or just human?