Do more rides, toughens bottom. You will be surprised at the change once you do 4 rides a week. I just use bib shorts, ditch the outer MTB shorts as they can crease and if its wet they hold water incresing bottom soreness (MTB shorts are a fashion item) I dont use cream during training I save it for event 😉 Clearly in the winter you may be better with water proof shorts or I use Endura single track trousers for training.
Gym ideal is a must, core, back, arms etc etc squats is your leg strength exercise. Basic exercise to increase strenght you need to pushing weights 70 to 80% of your max 6 or 8 reps X 8 or 6 sets works for me eg 6 reps X 8 sets or 8 reps X 6 reps all = 48 Gym is your recovery session you do between rides on your rest days. Should be at least two days apart.
Bike, try changin your position to more up right, add a spacer to stem, bring saddle forward a tad. Also try lowering the saddle nose for distance work.
Do back to back rides; 40km one day then 40km next day. Increase distances back to back until you get to @ 130 140km back to back then try out some near distance rides. Keep back to back training up, its tough but if you keep within your comfort zone you will be ok. Will improve stamina, endurance and toughen bottom. The idea is too keep within your comfort zone.
Rest is important when your doing back to back. Bed early, eat well. If your over weight then eat sensibly the training will soon burn it off.
Food and water. Train with the same food you will race on. Keep well hydrated. I make own power bars and train on water only. Will add a bit of electrolyte for multi day races.