pregnant? after penicillin

hi everyone would really love some advice i had tonsilitis and was put on penillin three weeks ago. foe the seven days after where your supposed to use extra precaution i forgot, i went to the doctor and he put me on the morning after pill. i took it and he said if your period is five days or more late to do a test. i was five days exactly late, test negative. now for the past few days i had achy breast and stomach cramps. i took a test this morning and i think i could see a line that was not there really. could hardly tell shall i just do another test in a few days? what you reckon the chances are? thanks xx