The dates of your intercourse do fall in the fertile window which is 14 days (+/- 4 days) prior to the next expected menses.
The symptoms of early
pregnancy - in first three months are:
1. Missing a period
2.
Nausea and vomiting
3. Frequency of urination
4. Breast Changes -
* Engorgement and tenderness
* Brownish discolouration of nipples and
areola. This happens in first pregnancy and is permanent change.
* Increasing the size of areola
* Clear secretions from nipple on squeezing
However, pregnancy is never diagnosed on any of these symptoms. For confirmation of pregnancy, clinical examination is necessary. To support the clinical diagnosis, urine pregnancy test and/or
ultrasonography after 8-10 days of missed period is performed.
Beta hCG test is highly specific and sensitive which can give reliable results within 2-3 days of missed period.
You must have realized that you have done your pregnancy test rather too early. Get your urine pregnancy test and/or ultrasonography done any time after 6th of April which will be reliable.
I hope you have got the answer for your query.