Not all hope is lost, there are several ways you can help your allies.
##By dealing non-physical damage
Magic weapons aren't the only way to bypass physical resistance/immunity.
You can achieve this effect by:
- Asking your party spellcasters to cast a relevant spell (such as Dragon's Breath)
- Utilizing environment features (pushing enemies in fire etc.)
- Using consumable items (e.g. Alchemist's Fire)
##By controling a battlefield Pushing, grappling, tripping - everything you can imagine. Unless you dumped your Strength ability score, it should not be a serious problem. ##By helping your allies to land an attack Using an action to help an ally will grant an advantage on their first attack, increasing effective dpr of your team as a whole. ##By provoking enemies to attack you/absorbing damage Essentialy by taking a tanky role, you will enable your teammates, if it isn't being effective, then I do not know what could be. Damage prevention is nearly equal to healing.
- Warding Bond is essential to keep your cleric alive.
- Taking Magic Initiate and choosing Compelled Duel allows you to draw enemies' agro just like in MMORPGs.
- Using a dodge action applies disadvantage to attacks against you and grants advantage on Dexterity saving throws.