Need help :)

I'll try to keep this short. I had a D&C a little over 3 weeks ago at only 6 weeks along with an empty sac. I bled for three days after the D&C. I immediately was feeling back to normal after the bleeding stopped and felt like my old self. I continued taking the cheaper pregnancy tests to see my HCG levels lower after the D&C. A week ago, I finally had an absolute negative on a cheap pregnancy test, what a relief! Well my husband and I started having unprotected intercourse immediately after the bleeding stopped and I was mentally ready. Well here I am about a week or so before I should start my period and Monday and Tuesday I experienced twinges and uterine cramps (not like a normal period cramp). Yesterday I woke up nauseated and feeling like I did before the D&C so i decided to take a test but I used the first response early detection instead of the cheaper test. Well there is a faint line but I don't know if it is still some HCG left from my D&C. Help?!?!? Also, I went for blood work yesterday and my HCG was at 25.5. The nurse has me scheduled to come back in a week to see if the level rises or falls. She said a level of 25 HCG could be a normal level for a pregnancy 3 weeks along. I'm so confused!! Any advice would help :) thanks!