Fainted line on test kit. Be pregnancy?

My girlfriend and i had sex during her periods using condom as protection on march 15th and 17th. Still, we took an i pill for more precaution on both days. Her last periods ended on 17th march and after that she had bleeding after 2 days and it continued for 4 days. Then we had sex on april 22nd and at that time few rounds were unprotected and few of them were using protection. Then she took an i pill on next morning(within 12hrs. Her periods takes  place around  1 month and 10 days. Now she did a pregnancy test on 3rd of May and it was negative. But after a week means 11th of may, the test had a very fainted second line. We did 3 test continuesly and all had very fainted line. Now we are so confused about it. Can someone suggedt what could be the possible reasons for this. She is not going and any medication. Is it could be pregnancy?