Mazal tov on the birth of your baby!
We are sorry to hear of your discomfort during relations.
In light of your physical pain, we would suggest that you see your gynecologist for an exam
You are correct that nursing can be associated with dryness. You may find that using a lubricant designed for relations, such as Astroglide or KY Jelly, reduces your discomfort. Taking time for foreplay can also reduce discomfort, since arousal is associated with natural lubrication. It is also possible that changing positions for relations could help make you more comfortable. A variety of positions are halachically permissible.
In addition to the above, when meeting with your gynecologist, you could discuss seeing a urogynecological physiotherapist therapist for an evaluation. The Center for Female Sexuality www.centerforfemalesexuality.com is one resource in the New York area. You could contact them or ask your gynecologist for a local referral. It takes courage to seek treatment for sexual difficulties. But we have seen many women benefit from such treatment when necessary.
Be'ezrat haShem, with appropriate assistance, your situation will indeed get better.