Hi Pauline,
You haven't stated your cycle length, but if it is the typical 28-day cycle, then 17 March would likely have been a fertile day.
On a typical test kit, there is a control line, and will always be shown if the kit is working properly. The complete absence of a second line would indicate a negative result, but a second line (even if faint) would be a positive result.
If "the other line is not clear", then it suggests the 2nd line is a faint one, and so positive. however, as it is faint, I suggest another test using 1st-morning urine. The first urine in the morning would have more concentration of hCG levels.
If you took the test properly and it was taken at least 21 days since your last sexual activity, then the result is likely to be reliable. However, you have not given much information.
- What were the start-dates of your last 6 periods?
- On what dates did you have sex since your last period?
- What date did you take the test?
You are your most fertile on OD, so why did you have sex then?
Emergency Contraception is to prevent ovulation, and you have to take the EC pill within (usually) 72 hours (3 days), although you can take EllaOne (where are you from?) within 120 hours (5 days). If he 'withdrew' well before his orgasm, there is a chance no sperm entered you, but some men do have sperm in their pre-cum.
You said, "We had unprocted sex after my period" but didn't state the date.
However, if the test you took on 26 April was taken correctly and at least 21 days after your last sex, then it is likely to be accurate.