Don't merge a pregnancy with other pregnancies.

1.3/source/RJW_Menstruation/RJW_Menstruation/Hediff_MultiplePregnancy.cs

@@ -731,6 +731,13 @@ namespace RJW_Menstruation
             if (pawn.Tile == -1) return "";
             return GenDate.DateFullStringWithHourAt(GenDate.TickGameToAbs((int)p_end_tick), Find.WorldGrid.LongLatOf(pawn.Tile));
         }
+
+        public override bool TryMergeWith(Hediff other)
+        {
+            if (other is Hediff_MultiplePregnancy preg)
+                return this.GetMenstruationComp() == preg.GetMenstruationComp();
+            else return base.TryMergeWith(other);
+        }
     }
 
     /// <summary>

changelogs.txt

@@ -1,6 +1,7 @@
 Version 1.0.7.3
  - Fix null reference error upon birth of female pawns.
  - Properly display multiple icons for pawns with multiple wombs.
+ - Fix only a single womb being able to become pregnant at a time. Requires multiple pregnancy enabled in the options.
  - Show the 'about to ovulate' icon in the womb dialog for induced ovulators during vaginal sex.
  - Display more insect eggs in a womb when someone has more, with new graphics by Euldrop.