Hi,
   Thanks for the query. I understand your concern.
    The spinning of head at 33 weeks of 
pregnancy can be due to blood pressure problems -
   - When the blood pressure is low, it still drops down in standing position (postural hypo tension ) this can lead to spinning.Iron replsacement before getting up is nor having any effect to stop the spinning .. but taking plenty of fluids with sugar & salt through along with all other medications advised would help.
   - 
High blood pressure can cause spinning with head ache. High blood pressure is concerning in pregnancy... Here bed rest/ restricting salts in diet/ positive tension freee mentality along with medications  suggested by doctor are helpful.
  - some times middle ear problems/ sinusitis/ allergic problems can lead to spinning( 
vertigo ) & treatment is very effective once the cause is found.
  - Many a times eye sight problems can cause such spinning.
  * In this context to visit your treating doctor & get serial blood pressure readings would diagnose type of BP High, low or normal ( Doctor may suggest to check urine for 
albumin.. in case BP is high ) ../ & check you for any other  cause for the spinning .
    Once the cause is known specific medications would control your problem.  -Please don't worry.
    Thanks.