Breastfeeding and periods

So im still breastfeedingmy 3 year old cut down to night's only,well my periods have not been the same since having my child and breastfeeding it took 11 months for my first period then skipped a few then eventually got a period once a month again for it to be only last 5 days well now it lasted 3 to 4 days first day heavy then day 2 light then 3rd day hardly anything.i have spoke to doctors but wasn't really helpful just they dont think it anything serious or menopause but worriedit could be premenopausal.the doctors wouldn't check me over as im still breastfeeding.my questionis is this normal for period to be like this as we would like to have another baby our 6th im 37