Hello
No, it can't be
As sperms doesn't stay in vaginas for any longer after the sex
it's not a store house for semen either

You need not to doubt in your wife, this could be due infection of urogenital tract like candida or other fungal or bacterial infection
Apart from infection , it can be physiological secretion of vagina are times

So you need not to worry
In my opinion you should consult your doctor preferably a gynaecologist for per vaginal examination and a battery of tests like vaginal swab culture and urine culture

Meanwhile Use condom during sex and maintain
good hygiene

Thanks and regards