It wasn’t clear to me whether you were asking about options for your current pregnancy or about family planning options for after the child is born.
To the first question, society will tell you that abortion is an “option,” but it’s not an option any more so than killing your four year old might be. Abortion destroys the life of a unique, fully-human child that you will never be able to replace. It is never acceptable. If you truly will not be able to feed the child, you could consider putting the child up for adoption, though I would probably worry about what type of message this would send to my other children. But there is no shame in accepting food stamps for the health and well-being of your children until you are able to get back on your feet.
You’re probably aware that the only legitimate methods of family planning that respect the marital act and the dignity of the man and woman are natural family planning methods and complete abstinence. Choosing to use contraception or sterilize yourself is a grave sin. My suggestion would be to consider learning a different method of NFP. If you were using Billings, learn Creighton or sympto-thermal. If you were using Creighton, learn Marquette. There are a number of different options you have, and some are easier to learn than others. If you decide you like the method of NFP you were using before but are now worried that you won’t do it effectively, consider taking a refresher course. A teacher can look at the chart for the month you conceived and help identify problem areas, whether they be interpreting the rules or drawing a coverline. It might give you some peace of mind to know that someone else is helping you interpret your charts.
I’ll pray for you. God bless.