Breastfeeding and dieting

I am breastfeeding my 4 month old and I am on the mini pill.

I am about 30 lbs from my pre pregnancy weight.

I walk about twice a week and try to do at least some exercises once a day.

I drink 100 oz-125 oz water daily.

But my problem seems to be my diet. I’m hungry all the time.

I don’t buy junk food. I try to keep fresh snacks in the house and healthy options.

I’m afraid to cut calories and lose supply. Does anyone have any suggestions or things that worked for them?

Are meal replacement shakes okay during breastfeeding? Like slimfast?