Can you get a girl pregnant with pre-cum if you have low sperm count and after smoking weed and after cumming once after oral sex?

Unlikely, but...: If the stars are aligned, the stars are aligned. Life can be full of surprises. A urine pregnancy test, done correctly, gives a reliable result 3 weeks after sex (3 weeks after when conception might have occurred), or 1 week after missing a period. If done sooner, a positive result is likely real, but a negative result may be due to testing too soon, and thus lead to a repeat test.