Young mother with spleen enlarged...Help me please!!?

I am 21 years old. Last summer i had a baby in september while i was pregnant i got kidney stones and while i was getting a sonogram of my kidney they noticed my spleen was enlarged so i went to a oncologist and found out that i had low blood platelets and then we waited till after the baby was born to do a Cat scan so by that point my spleen went back to normal size so he said it must have just been pregnancy so anyways its been 4 months. I went to the kidney specialist today and did another sonogram come to find out my spleen is enlarged again. Besides being a new mom and getting up at night with my son i am very tired and get bad head aches... I called the oncologist today and he reviewed my sonogram and he wants me to come in. So i have to wait till the end of may and i am just wondering if anyone has any idea what this could me i am a young mother and it is really hard to wait till may to find out.