They will go through periods of massing breeding to once in a blue moon.
Dont let that fool you.
If the female is receptive she will let the male breed year round 'when she wants it.'
Pairs will breed well for weeks than all of sudden look at each other like total strangers. Keep them apart for a while. Then when a big weather front moves through your area, put him back in with her and see if that doesnt stimulate some breeding.
When breeding it only takes once or twice a month to get a good lock up. The sperm will stay viable in the female for a long time. They dont need to lock up all the time to be successful. It only makes us feel better to see it more often.

What is her current behaviour?
Laying postion (coiled in a behive or kinda relaxed near the heat or cold side or wrapping the bowl)
Swelling is part of the normal "building" of follicles. If it only last for a day or two, then it very well could be the big "O". But if she is still looking bigger after a few days, she is probably just building them up. Which is another good sign. Means your on you way if all go wells.