Ttc periods been early and worrying

I've been ttc since last year. I had the mirena removed on June 23rd and had my first period 6 weeks after this in the august.cycles where abit dodgy for a couple of months after this but then where 35 days every month without doubt. However last month was 32 days and this month was 31 I'm really worrying that something's wrong. I have a 21 month old little girl. I'm still young and healthy  and so is my partner. Been drs is the past I was ovulating etc. Just really worried as my periods were so on time every month and now the past 2 months they've been different. Really worried and panicking that something may be wrong and I can't have any more children. Some advice and help would be very much appreciated. Thankyou in advance and baby dust to you all xx