My best advice is try to pick a specific time. I have add so I get the schedule thing and it may be hard to pick a specific time depending on your schedule. I find putting an alarm for each time I want to work out throughout the week helps me. Also doing it with someone else! Makes you feel obligated to do it since you included someone else. As far as the period thing goes it’s been a while for me so I can’t help too much but just do simple things. Even if it’s a 10 minute walk or 5 crunches just do smaller amounts or as much as you can. I know it’s hard to do but if you can power through whatever period symptoms working out actually helps relieve cramps and feels better.