Symptoms at the end of fertile window? Please help!

Is it possible to feel early signs towards the end of your fertile window? I am on my last day today and since sometime last night I have been having the worst tightening feelings in my lower stomach and it feels so uncomfortable and sore, I also feel as if I could throw up today but that could simply be the heat. I was told it's not possible but this is my first month ttc and I am so clueless and it's already messing with my head so much. Any help or advice with this or when you first started feeling symptoms and what were they would be so helpful!