When should we BD?

Jan • 27 yo, married for 5 years. TTC #1 beginning 01/16! Mostly paleo in diet but hardly ever pass up a donut.
My cycles are somewhat regular, but they vary just enough for me to wonder when the best time to try would be. My last few cycles have been 28, 32, and 30 days. Do we BD on day 14, 15, or 16, and what about days before and after? My doctor said every 2-3 days is best for healthy sperm so I'm not sure what to do.