seems from the history you give. Get a thyroid test,hemoglobin
estimation and sonography
done,to find out the reason fir irregularity in periods.
Repeat a urine pregnancy test with early morning urine sample n wait for five minutes and se that is there a faint pink line or not,as some times it comes v faint positive.
Any ways you are getting a sonography done which would tell whether you are pregnant or not.
Headache could be unrelated to pregnancy,n the fainting attack,can be due to hypoglycemia
or other reasons also like ectopic pregnancy but you would have other symptoms like,dizziness
,sudden colicky unbearable pain in the abdomen if it was ectopic n a positive pregnancy test also