Exercising whilst breastfeeding can be a thankless process. You may be doing it to loose weight, feel better, gain energy, have some time to yourself or just because you feel like you should. 

Everyone reacts very different to breastfeeding just as they do to pregnancy. Some put on weight whilst breastfeeding and can't loose it until they stop, others have painful joints because of the continued relaxin release in the body and some just have very hungry babies who 'take everything' on each feed. On this note it may feel that once an exercise session is completed then it is difficult to feed baby as the milk may not be there. I haven't even mentioned the sore boobs that are usually bigger than normal!. 

All this aside it is generally advised that pilates, yoga, swimming and maybe walking with the buggy are good choices of exercise. One way of making these feel more beneficial is to hold your pilates positioning during your walks and swims. Also pilates may be more beneficial than yoga because it will help to stabilise the joints during the continued release of relaxin... yoga may do the opposite if not prescribed appropriately.

Save the HiiT sessions for after breastfeeding has stopped. It is generally advised to wait 6 months postpartum. You'll have more energy and the benefits will be more obvious then. If done before the sessions should be low impact and done to a rhythm, not trying to push yourself through your limits. Sessions should ideally be done with a physio or highly experienced PT and you should have been checked over by one first. HiiT Pilates is perfect so that you can re-connect with your core in-between High Intensity sections. 

Most importantly enjoy your baby and BELIEVE that you will get your body back. After all I did after 3 babies and my approach was to chill for 1 year after each - hardly exercising at all except gentle pilates.