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. Warding Bond will help to keep your cleric alive. Taking Magic Initiate and choosing Compelled Duel will allow you to provoke enemies' agro just like in MMORPGs.